Is there a small amount of free movement of the handwheel?
Does the slow feed wheel move in and out as the handwheel is moved ?
Mill/drills like that usually have a clutch that engages the slow feed . Often just a pair of tapers , one on the slow pinion and one on the hand wheel, squeezed together by a bolt on the end of the hand wheel shaft.
Remove the bolt and slide off the handwheel, remove the worm wheel assembly . Clean and reassemble
Can the quill be moved up and down a little by hand (always a little backlash in the rack) ?
Check quill lock - often just a clamp squeezing a split in the quill bore. Carefully tap a wedge (flat blade of screwdriver) to spring the split open a tiny bit . Careful! You are not trying to bend it open , just release it a little to see if that frees the quill.
If none of the above...
Drop the quil out by removing the handwheel shaft and anti rotation screw - Careful when removing the spring, loosen the bolt holding the cap a few turns but do not remove . The cap has lugs that prevent rotation until pulled away from the seat - pul out and un wind carefully (refitting is the reverse precedure )
Clean, lubricate with light oil and reassemble