Since I brought it up I guess I'll throw in my (not even) two cents.
Yes, Grogu could learn how to build (or fix) a lightsaber, but he'd have to find 1 of the 3 remaining people that know how to build one. Luke, Ahsoka or Ezra. One of them he already left, one of them said she wouldn't train him and the third is still lost. Good luck, little guy.
If the armorer, or any other non-jedi finds a way to rebuild the thing just b/c, I will rant on these forums.
You don't think Gideon or some other Imperial wouldn't have spent years trying to figure out how to build more?