it's been a while since I stripped mine but if i remember correctly try this:
remove the upper hand guard buy pushing up the lever on the gas block (bit with rear sight on it)
the upper hand guard should lift up from the back and come free
then
loosen the allen grub screw where the metal part of the front hand guard is (where the sling loop is)
slide it forward and the wooden hand guard can be removed.
turn the AEG upside down and there should be a small allen grub holding the barrel to the gas block which was covered by the lower hand guard you just removed.
this should allow the front end to be removed from the receiver.
take off the pistol grip, remove the fake bolt handle including rod, spring etc which fits into the back of the gearbox (black button that holds the top cover on)
unscrew the screw that holds the selector lever on and remove the selector lever and bits.
gearbox should now pop out.
I think thats how it goes but I've got a mixture of inokatsu, guarder and VFC disassemblies in my head and I can't get to my Guarder at the moment to check but I'm sure it's this.