Can I change my mobile number at Twitch when I'm logged out?

I had some problems with my Twitch account and wanted to register again. The problem is, I have a new cell phone number and no longer have access to my old number. However, I get an SMS to register, but unfortunately sent to my old number and I did not change the cell phone number at Twitch. Means, the old number is still given there.
Can I somehow change my number to get my account back?

Did you write down the backup codes when you activated the two-factor authentication? If so, enter one of them and you can log in to change the number.

If you don't have the codes and haven't saved a second number either, it looks bad. Then you have to contact support and identify yourself if necessary, etc. Somehow let you identify that the account belongs to you. Unfortunately, I can't tell you exactly how this works with Twitch.