Ice is useful first off, hot & cold treatment might aid recovery too. Once the pains gone stretching very gently might be a thing to try. Massage can be benefitial (again done gently & make sure it doesn't irritate the problem area).
My next bit of advice is don't go crazy with a powerball again
There are probably safer ways for you get more strength in the wrist/forearm area, it might be that this "toy" isn't for you.
If it's general strength in the area you're after then you can get a bit of elastic that wraps around your fingers & practice finger extensions (an VERY underused muscle that will increase all your gripping moves), get a pair of "fairy balls", once you've mastered the basic circling moves aim at doing it palms down, both ways, that's quite hard, then once you've done that, buy another set & work at doing it with 3, then 4 balls (if your hands are big enough) VERY hard palms down!
You could also invest in a gripper, like a sports shop gripper & have a grip frenzy, or a CoC trainer if you're too strong. Try "catch grips". throw the gripper up in the air, catch & squeeze, no set up. nothing HARD, VERY VERY HARD! Even just getting a gripper & doing a 1 hand, no set-up grip is tougher than the normal way. Put a gripper on the table & using one hand just pick up & squeeze, no set up, no touching with the other hand, tough one.
There's 101 ways to strengthen your grip without risking your wrists with a powerball (I'm not saying powerballs are inherently bad, but it seems they are for YOU). Try out some other ways to train that area & have fun exploring some new toys