By far, the easiest way to unlock this is to play the 'Faction War' Game Mode - which I believe is a limited time game mode for around two weeks (but is bound to return at some point.) [Started 18/8/20]
Essentially, when teammates die they can roam around in a ghost-like form and when an enemy is defeated, they drop a respawn point. Have a teammate hop on it and you can revive them. It will most likely come through some form of natural gameplay but if you're determined just focus on being a medic. The respawn signs are littered around your HUD and Map.
After getting the achievement and grinding wins for the Legend achievement, I finished a game with 9 revives from just playing tactically.