How can I fix the guard on my mitre saw?
The parts list shows

M1 Blade Guard and Linkage     EV3BSM1 1
M2 Blade Guard Release Lever   EV3BSM2 1


From which I deduce that Wayfaring Stranger's comment is a good one to follow up. Your saw has a locking lever for the blade guard.

The User Guide also shows 2. Blade Guard Locking Lever



So maybe that lever is jammed/clogged or not in the position you thought it was?



If the lever moves but doesn't unlock the guard, you may be able to disassemble the guard, clean any sawdust and repair or replace any damaged or bent parts.