Trikopter support channel selection on Pixracer

Hi there

i have ha smal trikopter a quantum trifecta and want to get it fly.
but the majer problem is that the servo need to put on chanel 7 but the pixracer has only 6 so where do i put the servo ? can the parameters be changed so that i use chanel 1-4 and haave 2 aux options?

some pics of the project
all the 3D printed parts are developed from me
if there are intrests Pn me