Need some help with brake issue

yeah it can be tricky and messy. There are two ways for air to get out of the MC. You can tickle it out by dropping the front end of the MC and having it escape thru the C-ports.
Or you can crack the lines one atta time and push it out. But when you do that, you gotta slam the door before letting off the pedal, or the returning piston will just suck air at the fitting.
But take another look at the drawing. If your MC is upward slanting as they usually are, then you can drive the inter-piston fluid and air into the front reservoir thru the compensating port, by cracking the fitting at the front reservoir, badaboom!