If you would like to de-assign a swith on your aux switch you will need to access the System Mode>Aux SW menu within the TimeFactor OS and configure the corresponding switchs to a null mode or "- – -" within the menu selection. As a system default, TIP is assigned to BYP, T+R is assigned to TAP and RNG is assigned to repeat. Whatever footswitch that you presently do not want assigned just configure the parameter assignment to "- – -". So with regard to your situation, you will want to change the assignment so that it resembles this "RPT > – – -" There is not save function so once you have made the desired assignment you merely exit System Mode.
For more information on aux switch assignment, reference page 32 in the user manual.