where do I add my spousal support

If your separation or divorce decree was signed after 12/31/2018, then alimony (spousal support) is not entered on a federal 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

For divorce agreements dated January 1, 2019, or after you don't have to include information about alimony payments on your federal income tax returns since it isn't considered income or a deduction

For more information check here.