Water pumps are available on YT site at the link. Many serviceable water pumps are changed out when the engine coolant is drained and later refilled and the pump will not self prime. If that is the case post back.
See pic, you need to be between High & Direct, pull straight out and up for Low. As kenbob stated it can be ornery. Work it some and it will get easier. If that doesn't do it the cover may have been installed with the low range fork out of position (most likely) or the set screw in the fork may have backed off, or the fork is bent (not likely) or other possibilities that are not so easily corrected.