If it won’t go back up from the seat arm then it must be a safety edge or limit switch causing it… my money would be on a break in the footrest wiring. The trailing flex only supplies power and earthing plus a switched common and return and the two direction controls so shouldn’t stop direction movement(unless something is shorting).
If it’s working from the seat arm then you’ve only got 4 wires to work out, obviously identify live, neutral and earth and leave well alone as they must be correct.
The common feed will go to all the switches, the on/off feeding back via the common return. The up and down control switches activate when connected to the common by making one of the direction buttons on the remotes.