Mushrooms and ricordea don't react well to gluing, so you should get a small container, fill the bottom with a crushed coral type substrate, toss the shroom in, then put some sort of mesh over the top. Put the container in a low flow area of the tank, and eventually, the mushroom will grab a piece of the crushed coral. Then, apply superglue gel to one of your rocks, and put the mushroom on the spot of glue, then gently push down on the mushroom so that the piece of crushed coral sticks to the glue.