Look carefully, and one end of that pin will be smaller than the other. Use an appropriate punch at that end to drive the pin out, and the cover comes apart fairly easily.
Re-using it may not be possible, depending on how hard it is. To put the pieces back together, the pin has to be peened back into place either with a punch at one end, hard flat surface (anvil) on the other, or squishing the whole thing in a vise. May be easier to replace the pin (which may or may not affect the value if it's a collector's gun) than reuse the old one, which will likely look like it's been beaten on.