HELP w/ placement of headliner fasteners
 

I just had a new headliner put in, but instead of the original four push-pin
fasteners along the back edge the shop only put the two middle fasteners
back in place. Where the missing two fasteners on either side used to be is
now covered over with new headliner material. How do I find the correct
position to replace the missing fasteners? Is it safe enough for a
do-it-yourselfer to do?