Ok, so every time you turn on the machine your software settings tell it to perform a homing operation. Homing essentially sends the machine to a default starting position- your software describes this as being "work starting position" and the current setting is "mechanical origin" which is home position as set by the mechanical imit switches on X & Y.
Limit switches are not at BOTH ends of each axis so if you are homing in the wrong direction you will home to where there are no limit switches- that's why your machine keeps banging into the side- it's looking for a limit switch input that isn't forthcoming.
MAC reset position- I assume this stands for Machine Reset Position which is the same as homing. Your current setting is top right.... clearly this doesn't work so change settings one at a time and try to home the machine. When the right setting is picked the gantries will move towards the limit switches thus homing properly. Left- Top, Right- Top etc. describe positions which rely entirely upon how you interpret which is the front of your workbed and which is the back. If for example the Chinese manufacturer decides the area furthest away from the operator is the "front" of the machine and you think it should be called the "back" you can unwittingly home the machine the wrong way although your choice appears to make perfect sense to you.
Hope this info is helpful