I am filing MFS and my spouse didn't live in my home during the last six months of the year. Where do I add his home address so I don't have to include his AGI?

You do not enter anything about a spouse other than name and SSN on a separate return (unless you live in a community property state and must allocate income and then  you need the spouses incime, not AGI).

If you filed jointly in 2019 and are filing separately for 2020, you each must use the same total AGI from the joint 2019 return.  The mailing address on your return is irrelevant to this requirement.