How do I ask God for healing?

God is your father, you don't have to repeat a particular Bible verse, just pour out your heart while recounting his promises, Isaiah 53:5 says "by his stripes, we are healed." Have faith in God because "the prayer of faith shall save the sick," (James 5:15). God has the power to heal all his sons and daughters, commit yourself unto him, and you will receive whatever you ask (Matthew 7:7-8).