There is currently no way to heal yourself in Rainbow Six Mobile. However, if you are in DBNO (Down But Not Out) your teammates can get you back on your feet. DBNO is a state in which an Operator has lost all their health but hasn't died. Getting revived from DBNO sets you back up to 50hp, but you cannot go DBNO again that round.

Some game modes like Team Deathmatch feature health regeneration when out of combat.