I have bought a new casio Tk1550 and I am having trouble finding out how to apply flat plus and plus to groups. I saw on the reports how it will print them but could not find in the manual how to assign them. Any help in this matter would be appreciated.

It is normally listed under Flat PLU individual feature programming. Use the tables below it and you should see group link.
Some Casio user manuals don't go down to this level. If your manual doesn't have it, C-tech has the TK-1550 programming manual here:
http://the-checkout-tech.com/manuals/ca ... anual.html