Recently I bought a blue crawfish and it’s very active but one morning I saw it was on its back not moving but the antennas were I was worried that the other blue crawfish in the tank had attacked it or something or if it was moulting. it was fine in the night but in the morning it was like that I’m scared is it dead or not?
Carefully pick it up and see if it moves. If it doesn't move, it's probably dead.
You should also check the water quality for ammonia, nitrite and nitrate.
Do a 75% water change and gravel clean the substrate to remove anything in the water that might have caused the crayfish to die.
Make sure any new water is free of chlorine/ chloramine before it's added to the tank.