Is exercising with hand gripper helpful for tennis elbow condition?

Hand gripper: These are most suited to exercise and mobility of finger joints and wrist, not tennis elbow. When safe to go and see primary care provider, you can then have possible tennis elbow diagnosed and treatment options discussed.

Generally no: Exercising the muscles that open and close your fist while you are having tennis elbow pain can make your condition worse. NSAIDs, ice, rest, stretching and self massage can help. Physical or occupational therapy as well as corticosteroid injection can help once COVID clears enough that it's safe to go to your doctor.