There are many special achievements in "Warhammer 40,000: Space Marine 2", and releasing the monk is one of them. The requirement to complete this achievement is to force a snake to let go of the captured team members. This achievement says It's difficult, but not difficult, because very few people get caught.
How to release the monk achievement in Warhammer 40K Space Marine 2
Let go of the monk
Forcing a snake to let go of a captured party member
As shown in the picture, it is not difficult to say, but few people will be caught. You can discuss it with your teammates. If you are caught, hitting the snake will force him to let go.