If it's a cramp like fingers getting stuck in a particular position I use the other hand to move it the opposite way. Like fingers stuck straight out I bend them in with the other hand because I can't move the "stuck" hand. Once it gets "unstuck" I can usually flex away the rest of it by opening and closing the hand like I'm squeezing an imaginary stress ball.

All the above are great answers, but just want to be sure you're not describing a trigger thumb (painfully locks in the flexed or extended position), or even an electrolyte deficiency (if you take a water pill). Could we have more details, if any of the other suggestions written don't resolve the problem?

Don’t have that symptom yet but stretch and exercise for leg and back. Bummer!

It will go by. I have it several times.
Give it a massage and don’t think of it.

Hi Jessica, I think you got a lot of good answers & I hope they will get you figure to relax.🤗