Start with this Du'a
A'udhu billahi wa qudratihi: for pain in the body
بِسْمِ اللَّهِ، أَعُوذُ بِاللَّهِ وَقُدْرَتِهِ مِنْ شَرِّ مَا أَجِدُ وَأُحَاذِرُ
Bismillah (three times). A'udhu billahi wa qudratihi min sharri ma ajidu wa uhadhir (seven times).
“In the name of Allah. I seek refuge in Allah and in His power from the evil of what I feel and what I fear.”
Sahih Muslim 2202
Taught to 'Uthman ibn Abi al-'As when he complained of pain: place your hand where it hurts, say Bismillah three times, then the refuge seven times.