Can I use tuition assistance and the GI bill or it’s either or?

Your profile says you are retired, are you active duty?
If you're active duty you should go to the education center on your base, or email them.

If you are on active duty, the best route is tuition assistance. If you use your GI Bill while still in, you don't get the BAH benefit from it which means you would be throwing away thousands of dollars. You also most likely not be able to enroll with a full load, meaning it would drag out your education, potentially exhausting your GI Bill before you could finish your degree.
I would stick with tuition assistance for now, and work on the core curriculum classes that are required for all degrees, even look into CLEP testing (just be sure to check with whatever college you are attending to make sure they accept CLEP tests). Save the GI Bill for when you are out and ready to go full time.

TA for sure. If you use it all, you can use your GI Bill to help, or you can use em both if TA doesn't cover the cost completely, but as TSgt David Holman wrote - you don't get your BAH and stuff.
Best bet - use your TA and if you need a loan to help use that, and give the GI Bill to spouse/kids. You can use a TON of TA while in- Associates, Bachelor's, Master's, AND a Certificate.