How to fix bump in wall

Probably will need a sander to level out

Is it an outside wall? I have an outside wall that did that and putting a deflector on the air vent that was blowing up, under it did the trick. Condensation from the temperature change.

Cut the sheetrock out and replace it either, just the space that's bad or a whole new panel of sheetrock.

I think this will help you out! https://www.youtube.com/watch?v=x_MC7JLnV9o

Press on it and see if it moves in an out. If it does, it has come loose from the lath. The only way to repair it is to remove the affected plaster and clean out the slots in the lath. Sometimes horse tail hair was used to strengthen the plaster. If that is the case, it must be cut around the bulge but not the lath. You can re-plaster with mortar mix pushed into the slots so it's a little shallower than the wall. After it cures, a thin layer of drywall plaster will give a smooth surface that can be lightly sanded for a blemish free surface.

Roland's solution is the way to go. Make sure you wet the lath with a damp sponge so it won't suck the water out of the mortar or it won't cure properly. The lath will be brittle dry.

I want to hug and kiss Roland!!! Excellent! thanks for sharing your knowledge, hands on experience is invaluable.