How do I print the back side of my Form 1040? When I print my completer tax forms, page 2 of Form 1040 is missing. All the other pages print.

The 1040 form was completely revised in 2018 and it is now only 23 lines long.  It is now a 1/2 page length two sided form, so both pages of it print on one side of an 8 1/2 x 11 sheet of paper.  If you look at the printout of your return, you will see the signature line in the middle of the page as that is actually the bottom of page 1 of the form.

See this IRS PDF of the form:  IRS Form 1040