How do I change income and withholding for 2023? I lost my job.

Why or where do you need to enter that?  You will get a W2 in January from your job.  You only enter the W2.  You don't need to report that you stopped working.  The 2023 Online versions won't open for several weeks.  And you need to wait to get the W2.  

There is nothing to enter now about losing your job.   Your former employer has to issue a W-2 to you by the end of January that will show what you earned and had withheld during 2023; that is what you will enter into the software.   Make sure the employer knows where to send your W-2.

 If you have been receiving any unemployment compensation, you will also need to enter a 1099G for that---unemployment is taxable income on your federal tax return.    Some states send out the 1099g but many of them expect you to just get it from the unemployment website yourself using the same password, etc. you have been using to certify for weekly benefits.