Use an old key that fits the lock and insert it into the lock leaving just a few mm sticking out, dont push it fully home.
Then apply light pressure in the direction needed to open it and tap the key in to the lock on it end using something like a thin piece of wood, like a spoon or suchlike whilst maintaining the twist.
If youre lucky it may "bump" the lock open.
Dont hit the key hard tho, just tap it in while turning it lightly.
Only other way is to make a small tension wrench and apply a very light constant pressure to the lock whilst stroking the pins to make them pop one at a time.
Takes a while to develop the feel but if the locks worn you stand a good chance of doing it without damaging anything.
