Hey there,
Clean your iPhone immediately if it comes into contact with contaminants that might cause stains, such as ink, dyes, makeup, dirt, food, oils, and lotions. To clean your iPhone, unplug all cables and turn it off. Use a soft, slightly damp, lint-free cloth. Avoid getting moisture in openings. Don't use window cleaners, household cleaners, compressed air, aerosol sprays, solvents, ammonia, or abrasives to clean your iPhone. The front glass surfaces have an oleophobic coating. To remove fingerprints, wipe these surfaces with a soft, lint-free cloth. The ability of this coating to repel oil will diminish over time with normal use, and rubbing the screen with an abrasive material will further diminish its effect and might scratch the glass.
To clean the Home button (allowing Touch ID to work optimally), wipe it with a soft lint-free cloth.
if you still need help I will advise you to go to Apple center or AASP (Apple Authorized Service provider) to help you, you can find the nearest one by this link ☞ Apple - Find Locations