One simple fix would be to move the VIs to the same folders that they were installed on the original pc. If you don't want to do that, then when you open the main VI, it should prompt you for the missing ones. All you have to do then is browse to the new locations. You would then save the modified main VI.
If you have already saved the main VI with the subVIs missing, go to the diagram, right click on the blank VI, and select Replace>Select a VI and browse to where they are.