Black shoe for track of casement window

Hi there, I am having trouble assessing my next steps as I attempt to repair my casement window. The mechanism to the right is the original and was "slipping" as I attempted to close it. So I ordered the single arm to the right. However I can figure out how to either find a replacement or remove the original and re-install the black shoe for the window track. It says "Truth" and "29" on one side and USA on the other. Any guidance is much appreciated. Thank you.