iPhone fitness app not working

I can see my activity on my watch, but when I try to open the fitness app on my iPhone 12 promax it’s a black screen with the rainbow rings with the message “the fitness app works with Apple Watch to keep track of your activity and workout history. To start using the app on your iPhone, first set up activity on your Apple Watch.” I have tried everything I have seen on online forums but nothing has fixed it so far. Any suggestions?