You must save 3 teammates with the grip ability without dying yourself (in the same round). I pulled teammates back from the choke as it was indicated they needed healing. However, it’s entirely possible that the bubble which surrounds them prevented their death thus constituting a save. My video:
Lifeweaver Cute & Pixel Spray Guide: Giving Tree & Life Weaving Achievement
I did this in role queue quick play, it may work in open queue (should), but thankfully there aren’t further glitches which plagued other OW2 heroes ok release.
EDIT: Reports are that you should aim to have the bubble absorb enough damage that it would have otherwise killed your teammate. So for example pulling them out of Bastion fire with low health while Bastion continues to shoot the bubble should count as a save. The further away a teammate is, the longer the bubble is up as it pulls them away and therefore the greater the opportunity for it absorb more damage.