Makita saw cannot adjust height

I have a Makita worm drive saw Model #.5007NB.  The plate will not lock because there is a bolt head on the locking adjustment mechanism that will not tighten.  Yjr lt heaad will not turn when I try to tighten it with a wrench.  How can I get this tight?

Thanks,

GB

Pop off the c clip , take off the lever then tighten the nut until it is tight enough to hold but not too tight that you can’t use the lever to loosen it. Then put the lever back on and pop the c clip back on.