Mushroom dun like high flow, so place it at high flow area n wait for it to detact itself. Or use a pen knife slowly cut the base which attached to the rock. The cutting point must be as near to the rock as possible.
Use super glue gel to glue the base of the mushroom slowly and gentlely to the desired LR(not to apply too much). This action is done out of the water ! After gluing, wait for 1~2 minutes then put it into low flow area over nite for it to stable.