See if the junction box has a neutral wire in it (white) as you will need that to get 2 ea 120VAC legs out of the 220 VAC. (pleas don't use the ground wire to provide the neutral connection).
A 220 circuit should have a dual breaker with the two toggles connected together so they both switch off is one side overloads. You don't need this for 120VAC, but it just means that if on 120VAC side shorts you will lose both legs.
A 20amp 120VAC circuit will have a different outlet rating that indicates the higher power available. The main concern with higher power circuits is that the wire is sized to handle the power, you already have this in place. If you have a high amp breaker 40,60 amp, you should change it out for a regular one, you can leave the wiring intact. You want the breaker to blow when something goes wrong, sometimes things go enough wrong to cause a problem without a dead short to blow the breaker.
Generally speaking you want the breaker sized to handle the expected load and not totally over spec'd
Have done lots of wiring, but not "certified" in anything