Depending on the material your floor flange is attached to what your supposed to do.
If it is lead you normally solder it to the brass flange
If it is cast Iron you caulk it with lead and Oakum
If it is No Hub Cast Iron you just tighten down on the flange nuts.
If it plastic crap your SOL and best bet is to try to put lead shields into the cement floor to anchor this defect in materials and so called workmanship. BUT as the stumblebums say PLASTIC is the new CHEEEP way of dabbling in plumbing….