I have a 3 unit bridge. A small part of the metal has broken and floss can go through. Any suggestions?

Removing
a permanently cemented bridge to attempt a repair is tricky at best. There’s a
real risk of damaging the abutment teeth while trying to remove the bridge. The
fit of a repaired bridge could be questionable as well. I think the best long term
choice here is to cut off the bridge and do a new one.

If you can floss through the bridge, there is nothing you can do to fix it.  Right now, it is a big danger to the abutment teeth holding it up because the false tooth becomes a lever torquing on the tooth it is fastened to and can easily break that tooth.  Then you get an even bigger bridge.  Best to get it replaced ASAP

If you are comfortable going without the bridge in the mouth for a few days I would suggest you see your current dentist and have him/her remove the existing bridge and send it in to the laboratory for repair. In the event that the bridge is in the front and visible to the public another option would be to have you go directly to laboratory for the repair. Best of luck hope all works in your favor.