Mrthdrb

Imagine that you're saying something, but then realise you want to say something else instead. In English, you might say:

I don't like ice cream, because— actually, no. I like chocolate ice cream, but I don't find other flavours tasty.

How would this usually be done when speaking in German?

You can choose one of the following. I'd say that "wobei" is the more common one and actually expresses the change of mind, but the other formulation ("oh wait!") is also in use.

Ich mag kein Eis, weil ... wobei (stimmt gar nicht), ich mag Schokoladeneis, aber die anderen Sorten nicht.

Ich mag kein Eis, weil ... warte mal (stimmt gar nicht), ich mag Schokoladeneis, aber die anderen Sorten nicht

The (stimmt gar nicht) can be omitted. If used, it puts even more emphasis, that the previously started sentence is not true.

We also use »das heißt«, often abbreviated by »d. h.«.

Ich mag kein Eis, weil – das heißt, nein, ich mag Schokoladeneis, aber die anderen Sorten nicht.

Another valid part of the correction culture is the particle »äh«.

»Martin, wie viele Schnäpse sind noch da?«

»Vier, äh, fünf!«

Ich will, äh, ich kann nicht helfen!

There are many ways to change your mind mid-sentence, just like in English. You gave one example. I'll try to give a few examples for German. Some of them probably overlap with the answer already given:

Original:

I don't like ice cream, because— actually, no. I like chocolate ice cream, but I don't find other flavours tasty.

Possible translations:

Ich mag kein Eis, weil... oder eigentlich doch: ich mag Schokoladeneis, aber ich mag die anderen Sorten nicht.

Alternatives:

Ich mag kein Eis, weil... Das heißt, schon: ich mag etc.

Ich mag kein Eis, weil... Wobei, ich mag etc.

Ich mag kein Eis, weil... Allerdings, ich mag eigentlich schon etc.

Ich mag kein Eis, weil... Dennoch, ich mag schon etc...

Ich mag kein Eis, weil... Oder eigentlich schon: ich mag etc.

Ich mag kein Eis, weil... Ja ja, ich mag eigentlich schon etc.

Ich mag kein Eis, weil... Obwohl, (doch,) ich mag etc.

Ich mag kein Eis, weil... Äh, das stimmt nicht, ich mag schon etc.

Ich mag kein Eis, weil... Korrektur! Ich mag schon etc.

Ich mag kein Eis, weil... Oder doch, Ich mag etc.

Ich mag kein Eis, weil... Obwohl/na ja/oder, das stimmt nicht ganz. Ich mag schon etc.

Ich mag kein Eis, weil... Äh, falsch! Ich mag etc.

Ich mag kein Eis, weil... Warte mal, ich mag schon etc.

Ich mag kein Eis, weil... Genaugenommen, ich mag schon etc.

I'm sure I forgot some, but as you can see, there are many ways to indicate you changed your mind, mid-sentence or not. As you can also see, you can mix some of them too, i.e. the words schon, doch, eigentlich, etc. can be mixed in in most of the alternatives.

From the above mentioned I would deeply encourage the use of "wobei" as it is an adverb which is beautiful but deminishing in use. The same as with "dennoch".

Though "Wobei" means: "Bei welcher Sache". Which can be used in all kinds of cases. If you look in the Duden you'll find this one for instance: "There's nothing he finds joy in anymore." Which would translate to: "Es gibt nichts mehr, wobei er noch Spaß findet."

To compare it with the OP's original phrase I would use of the above mentioned "das heißt" or "eigentlich/im Grunde":
"I don't like ice cream, because— actually, no. I like chocolate ice cream, but I don't find other flavours tasty."
"Ich mag kein Eis, weil - eigentlich, nein. Ich mag Schokoladeneis..."
"Ich mag kein Eis, weil - im Grunde, nein. Ich mag Schokoladeneis..."

"Eigentlich/im Grunde" pretty much always nail the meaning of "actually". Sorry for being nitpicky but I find it important to point out that the marked answer has additional use cases and despite its beauty the word "wobei" does not translate the "actual" meaning of "actually". And should not be learned as a substitution.

Furthermore it should be pointed out that Germans would additionally change the "nein" to "doch" -> "eigentlich, doch! Ich mag Eis..." "Doch" is an adverb which negates an aforementioned negative statement.

It's used as such:

a: Go clean your room!

b: No! <-- negative statement

a: Yes!

--- German

a: Räume dein Zimmer auf!

b: Nein! <-- negative statement

a: Doch!

Or:
a: Bayern Munich will not win the cup this year. ** <-- negative statement **

b: No Bayern Munich will be champion again.

a: Bayern München wird dieses Jahr nicht wieder gewinnen. ** <-- negative statement**

b: Doch! Bayern München wird wieder Meister.

Hasn't been mentioned yet, so I want to add it. I have little formal education in German, but am a native speaker and my instincts tell me "obwohl", as in

Ich möchte eigentlich nicht essen gehen, obwohl... Beim Italiener hat es mir letztes Mal echt gut geschmeckt.

In particular, I'd use "obwohl" to indicate that I have some doubt about what I said, then follow up with a thoughtful pause to indicate that I'm rethinking my position.