Hi rob and welcome to the beginners section,
Fish sitting on the substrate can be a sign that the water chemistry is not healthy for them, although it could be other things too, but that's the most important thing for us to worry about first!
The members will need you to feed them more information so that they can help you better.
What is the tank size?
How long has the tank had water in it?
When were fish first introduced?
How was the tank cycled?
How many, what size and what types of fish are in the tank?
Do you have a liquid-reagent based test kit and if so, what are the ammonia, nitrite(NO2) and nitrate(NO3) levels?
What is the pH?
How often has water been changed in the tank and what percentage is usually changed?
It may be very important to do a large water change if there's a possibility that ammonia and nitrite(NO2) might be in the tank water and even answering the above questions shouldn't get in the way of that. But if the tank has been running for a year with no water changes it might be important that the water change not be large, so we do need to know that part first. When water changes are performed, the return water should be conditioned (with a product that removes chlorine/chloramine) and roughly temperature matched (your hand is good enough.)
~~waterdrop~~
