With the barrel already off you push the foregrip forward so that the forend action bar bolt group will slide out from the receiver. Using a punch, tap out the two trigger guard retaining pins and remove the trigger assembly.
To reassemble, make sure the hammer is cocked, re-install the trigger assembly in the housing and reinsert the pins. Reinstall the breech bolt group on the action bar and slide the forgrip back onto the mag tube until the bolt slides into the receiver.