What kind of parts do you have, or are you playing sandbox? If you have the claw on the rover, you can grab the stranded vessel and pump fuel into it by right-clicking on its tank, alt-right-clicking on the ship's tanks, and telling it to transfer fuel. But actually, it might be easier to just fly another ship there to give them a ride. Unless you land very nearby, driving across Mun in a rover always takes much longer than you think it will, and that's assuming you don't crash long the way.