Either select T-Shirt Transfer paper from the printer options when selecting
the type of paper.. which will automatically print a mirrored image on the
sheet
or
Use a graphics program to 'flip' the image then save that 'flipped' image
and print it.
This is only valid for t-shirt paper for LIGHT colored shirts. If you are
using the specialist dark t-shirt transfer paper, the image does NOT have to
be 'flipped' as the method of transferring it to the t-shirt is different.
It is peeled off the backing paper and put on the t-shirt the right way up.