First, do as many exercises as you can that work your grip automatically while you’re training something else. Start doing deadlifts, one-arm dumbbell rows, farmer’s walks, and shrugs. Avoid using straps on these exercises so that your hands have to work their hardest. Focusing on making your training harder rather than easier is probably enough alone to remedy the problem.
If after a few weeks you still can’t crunch your empty protein-drink can, add some moves that train your grip directly, like plate pinches: Squeeze two 10-pound plates together, smooth sides facing out, using just your fingertips and thumbs. Hold for as long as you can; repeat for three sets. Work your way up to more plates and longer times until your handshake can crush bone.