Activate the form by entering the year at the top of the 1040x, then start making the changes needed (if you make changes then activate the 1040x, the original figures will not flow over to it)....and the original amounts wont populate until youve made a change that changes the figures on the return.

If you've already made extensive changes that would be a huge chore to un-do and re-do, then you can just type the original figures into the Original column of the 1040X...that will work as well.