It just takes time and practice. It seems impossible for a while until all of a sudden you’re doing it. That’s just how learning guitar goes. The more you practice the more dexterity and accuracy you build with your fingers. My recommendation is to learn how to play a G chord and a D chord. Strum G 4 times on beat and switch to a D to strum 4 times. Keep going back and forth until you can reliably not miss a beat during the transition. Then do it with two other chords and then two others. You’ll learn the shapes, build dexterity, and muscle memory. It’ll be way off beat and sound like crap at first. Keep it up and within a week or two you’ll be good to go.