If the divorce or separation agreement was executed after December 31, 2018 then any alimony received is not reported on a tax return.
Otherwise -
To enter Alimony payments received -
Click on Federal Taxes (Personal using Home and Business)
Click on Wages and Income (Personal Income using Home and Business)
Click on I'll choose what I work on (if shown)
Scroll down to Less Common Income
On Alimony Received, click the start or update button