The trick is to get your hands on auto-pilot. Which is another way to word what Robin stated. This takes time. Start by vamping (staying) on one chord with an easy strum pattern. It can be the island strum or something simple like:
Record yourself. Try talking over it. Go back and listen to see if you kept it steady and didn’t mess up the pattern. If you made a mistake, try to analyze your performance and figure out what’s tripping you. You can even post it here. We’d be happy to watch it to offer more feedback.
Run this exercise everyday. And try singing simple melody lines too. That way it’s not just “hello, I am talking” while you strum LOL
Keep at it. It takes time, but you’ll get it!