I cannot change my pedals because of a plastic cap
Not all pedals have hex-socket insets on them.  This is especially true for cheap pedals that come on some bikes.
You should invest in a proper pedal tool, which is a 15 mm wrench with a narrow profile, widely available from tool manufacturers. If you look closely at the area between the pedal itself and the crank you will see two small &quot;flats&quot; or &quot;lands&quot;.  This is where the pedal tool fits and you can then tighten or loosen it.