Disc brakes are of 2 basic types. On some (most mechanical) only one puck moves, and on others, (most hydraulic) both move.

What you need to to is adjust the brake according to this basic design. If only one puck moves, adjust so the stationary puck just clears, then use the cable adjuster tor the moving one. If both move, the easiest way is to loosen the entire brake, apply brake forcke so it clamps to the disc, then tighten it in that position. When released both pucks should move off to decent clearance.

Two things that make adjusting harder are a warped disc, which like a warped bike wheel needs more clearance to not rub at the high spots. The other is a caliper not squared up to match the disc. This has the disc running between the pucks at an angle, and rubbing in back on one, and in front on the other. Since total travel is small, it's important that everything is straight and square.