A voluntary system encourages you to record your sexual partners within grindr. Maybe when you meet up you scan a QR code, that then logs that those two users have had contact, in the event that one of those users contracts an STD they can click a button that notifies the other user/s they have tested positive. Because honestly trying to remember every guy you slept with with and find them on Grindr again to let the know isn't easy. This also alleviates the need for those awkward conversations. Then the data resets every time you update your last tested date in your profile.
Plus it would also make for an entertaining Grindr wrapped, all anonymous obviously.