Un hook the cable at the arm . Swing the arm forward, where does it stop, take a picture. Grab it with pliers and try to move it forward if it stopped. It should have spring tension on it. If not somtbing is not engaged correctly. Pull the cover.
If there is spring tension, take the arm off the shaft. Rotate the shaft forward until it stops. Check cable for any drag it shoukd move easily amd freely. If not replace or lubricate with wd40. Adjust the cable at the threaded adjuster on the cover to the middle . Place cable end into arm and slide it onto shaft with the cable as tight as you can by hand. Bolt it on re adjust slack to 2 mm at the hand lever. Should be good if its slow