Well.An easter bunny with a hat(Scarlett) has to give you a quest 1 . for you to do that :p.After that head over to the plant and and press whatever button you use on phone to interact with things(ye i have no idea what phone controls are for this:P). Then it should give you an option if you want to sacrifice your behind.Basically this:
(Tho if you already accepted a quest and did every thing i told ya,and it still doesnt work.Then it might be a pesky bug :P.Or it could be different on phone,as this are pictures from a pc version of the game,but eh idk).