Try tightening the leg screws.  If that doesn't work, re-glue the
legs with West System epoxy.  This is not the time, in my view, to
be historically accurate with the choice of adhesive (for other jobs,
yes).  Some of my piano leg repair customers had infants crawling
around under the piano.

I usually separate all glue joints which have play in them.  Sometimes
I use a rubber mallet to separate them.  Clean old hide glue off with
a chisel and sandpaper, vacuum out dust and wipe down with solvent.

I follow directions on the West System can for mixing and application.
Tightening the clamps enough but, not too much, as this could "starve"
the joints of adhesive in some instances, making the joints weaker.
Excess epoxy can be cleaned off with acetone before it dries.

I use an old automobile bumper jack to raise the piano to remove the
legs, which can be a challenge with the drawer underneath.  The drawer
may have to be removed.  Repair the legs one at a time.  Place the bench
with a pile of books on it, underneath the piano as a backup to the
bumper jack.  If your bench or something similar is _really_ sturdy,
you can try lifting the piano sliding the bench and a pile of books to
hold up the piano, relying on that.

A big _warning:_ this can be risky.  If unsure, have the job done
professionally.  I have found most regular piano technicians love tuning
and things like that, but are not "great" at wood repairs and may think
they are, so choose wisely if having the work done professionally.  Get
a trade reference for a piano technician who is very good at woodworking.
Re-repairing "unwisely done" gluing jobs is difficult and costly.

It may even be necessary to have piano movers place the piano on its
side and set it back up after leg repairs, if more than one leg needs
gluing and the piano technician does not live close by.

Bill Maguire