My wife have rheumatoid arthritis. Is there a tax credit for this? If so can I still amend my 2022 tax return?

There is not a tax credit available for people with rheumatoid arthritis.  

However, if you use itemized deductions and you have paid out of pocket medical expenses that exceed 7.5% of your Adjusted Gross Income (AGI), then you may get a tax benefit for claiming those expenses.  If you have already filed your return, you can amend it to include medical expenses if necessary.