Before you can teach your dog to roll over, they need to know the "down" command. Once your dog is consistently laying down on command, you can start working on the roll over.
Hold a treat in your hand and lure your dog into a sitting position. Once they are sitting, slowly move the treat over their head and towards their shoulder.
As soon as your dog rolls over, mark the behavior with a verbal cue like "yes" or "good" and give them a treat.
It may take some time for your dog to learn the roll over trick. Be patient and consistent with your training, and eventually your dog will get it.
If your dog is having trouble learning the roll over trick, you can break it down into smaller steps.
Using a variety of treats can help to keep your dog motivated during training. Try using different flavors, textures, and sizes of treats to see what your dog likes best.
Training should be fun for both you and your dog. If your dog is getting bored or frustrated, take a break and come back to it later.