"Pedal assist" can mean a torque sensor, or a PAS sensor based on pedal revolutions, or "revs". You want a throttle.
If your controller has a connection for a throttle, then, yes, you can. If not, then you need a new controller, and also some investigation to see if any custom hardware has been added to prevent the addition of a throttle. Likely not.
Looks like a German motor in a custom frame, possibly one of the new Bafangs. Germans use custom controllers and replacement is difficult if not impossible. Bafang uses internal controller which can be replaced if needed but is a complex procedure that is not recommended for an amateur.
These are matters which should be investigated thoroughly BEFORE purchase. Did you buy it because it was a pretty color?