When you rebuild something, you reassemble it. You might find that taking apart your bicycle is easy. but things may get much more complicated when you try to reassemble it.
After you remove the legs from your kitchen table so you can move it through a narrow door into another room, you'll have to reassemble it. You can also use this verb to mean "gather together again," like when your art class visits a museum, where the students spread out to see different exhibits and then reassemble in the lobby later in the day.