pedals only, i thought handlebar, seatpost or worst frame. Okay 2 things u can do:
1) check that loose pedal, on the pedal theres should be a marking or whether its L (left) or R (right). It should be R (right side). if its not, check the other pedal, if its R, then the mechanic is reversed the order, take both out and re screw it in.
2) the drive side is suppose to be screwed clockwise when tightening. use size 15 spanner
if both still fail, go back there lor, still under warranty and your bike is foldie. not so bad