That’s crazy, every GV i’ve laid hands on both older and newer ones including customer bikes, always had a screw at the back to remove the orange lense cover off.
I suspect you have an aftermarket version ?   (unless you’re the only owner and the bike has never had its indicators changed?
Or try a guitar pick to pry it open , but i warn you, if it won’t budge, don’t force it as it will snap the lens of!  (unless its an aftermarket version that was glued in after they fitted a bulb inside.)
or try to “unscrew” the cap and see.  (Could be a newer twist & lock type)
Look at the snap shot below, this is the real assembly of the tail light unit and bulb is 10 watts (max!!)
