The admins of that group need to kick the dictator off , as admins they can do that , as long as he isn’t the sole admin with them being moderators.
I had a funny experience with a Facebook page from my old hometown which was run by three very nice ladies who added on a guy who turned out to be a real Nazi by removing them from the page they started ( 5000 members) and made himself the sole admin.
I ingratiated myself to him and offered to help , he then made me an admin but the trouble is he didn’t know I was secretly working with the ladies.
After my Facebook probation period I arseholed him, invited the three ladies back on , then appointed them admins and resigned from the page.
You should have seen the death threats he sent me following that , harassed me for weeks .
But I had the last laugh didn’t I !!
That’s what someone needs to do to that fella.