Undo or revert transforms

Select Edit > Undo (or press Ctrl+Z) to step back through previous transformations.

You can also return an object to its original location on import as follows:

Select the objects you want to work with.
If you want to revert all transformations made to a model, marquee-select the whole model so that all its objects are selected. To select all objects in a hierarchy, use the Organizer (Edit > Organizer).
Select Edit > Transform > Revert Transform.
The selected objects are returned to the original position, rotation, and scale of the model when it was imported.