You cannot adjust them firm, you need to get all the air out of the fluid. The quickest way is to push the brake caliper against the brake disc (by hand) to move the brake piston in. Pump it back out with the brake pedal, and repeat until you have a firm pedal, usually 2-5 cycles will do. If the pedal will not move the piston back, you have so much air inside that you first need to air the system the usual way. Check out Youtube for tips if uncertain.