Hardware and Fasteners - Fuhr door handle loose

I have old Fuhr door handles on a swing door to my patio that are loose. Can I unscrew the plate from the door and somehow tighten the outside and inside handles into the door (if so, how?) -- or can I replace the handles (is so, with which brand since Fuhr handles are no longer sold in stores as far as I can tell)?

The metal plate that holds the handles into the door is 8-1/2" long and 1-1/4" wide. The door is 1-5/8" wide. The metal section with "Fuhr" stamped on it that is in the middle of the door is 5/8" wide.

Thank you.

Not familiar with the brand, but by your description, you have levers, rather than knobs, and levers are typically held to the spindle (the shaft that goes through the door) with a "set" screw, in the inner lever...it may be quite small, possibly a socket or allen screw. These screws are always comming loose on this type of lock.

You can purchase Hoppe brand handles to replace Fuhr products, I believe.