Thanks for the explanation. At least it is a solid base of a laser machine, if I have understood it correctly, so you have the possibility to restore/upgrade the machine.
The calibration tool I mentioned is this one.
(I have however removed the copper cross on one tool, and changed it so that I also have the opportunity to insert my targets on the Z axis)
If you want my target file, please tell me
Possibly you have a completely different mirror holder system like most Chinese machines, in this case it needs to be adapted.