You will need a bench clamp, screwdriver and two plugs. One for each port.
Fill the master and place it in a bench. Start with the rear outlet port (the port furthest away from the plunger).
Push in the plunger. While doing so crack the rear outlet port to remove air. When the plunger is all the way in close the port. Repeat until all air is gone.
Do the same with the opposite end. The repeat at least once to confirm.
When re-installing the master try to get it back in with minimum leaking.
When done you will need to bleed the whole system. Start with the passenger side rear, then drivers side rear, passengers side front and drivers side front...