Out of Trim, which version of FM are you using, the airline one of the Handling agent one? Altea is an open architecture system and most parameters can be set as required by the user.
If it’s the airline version you are using then the airline have chosen STD-15 for the load sheet and you cant change it. If its the handling agent system then you need to talk to your DCS coordinator.
It’s a bit alarming you have to use a system with no training and no manual!