U can try to very slowly turn the center screw loose only about an eighth of a turn while you hold the handle steady with your other hand. U want to turn the screw just enough to get a small separation from the handle. Then pull the handle out towards u filling the space u made when loosening the screw. Then while pulling the handle out towards you tighten the screw. If theres a packing nut and its just rust stopping it that should fix it. If its not that its the gate is rusted out or broken and will have to be replaced.