Set your fullbacks to normal mentality, run forward often, run with ball normal and cross ball often.. If they are good at dribbling you can set them to cross from byline.. If you have a targetman with great jump, header and bravery then set them to aim for him and set targetman supply to head in team instr.
If you want your fullbacks to overlap your wingers, then simply use the individual mentality i mentioned and set your team instructions to wide and focus passing down both flanks
Give them a forward arrow to the wingback position
This works when it comes to overlapping and crosses/assists for the fullbacks