How to convert 240 receptacle to 120?
So you have a 4 wire feed if the barely wire was the bare copper. First you will need to open the panel and verify the neutral is tied to the neutral buss. Next you will need to install ether a single pole 20 amp breaker or a common trip double pole 20 amp breaker. Now if you used a double pole you will have 2 ea 120v circuits wire the black white and ground to 1 outlet and the same white pig tailed, red and ground to a second outlet both circuits share the ground and neutral the neutral will not be overloaded because they are sperate legs that are 180 out of phase with each other. If you only want 1 circuit a single breaker just cap the red or the black at each end.  I suggested a 20 amp breaker because most of the 240v outlets are 30 amp or larger using #10 wire or larger. If the wiring is larger than #10 you will need to pigtail the larger wire with #10 or #12awg because 120v outlets usually are only listed for #10 awg max. Last depending on the location you may need GFCI protection, multi wire circuits sometimes do have problems with MWBC's. Make sure that the neutral is split, or pig tailed prior to the gfci's or the first outlet will trip every time the second outlet is used you can even break the bridge connector on the outlet hot side of a duplex outlet and have 1 circuit on the top outlet and the other circuit on the bottom outlet, this is how I have wired many kitchens in the past.