I have recently purchased a DS7 Crossback registered April 2022
How do I update touchscreen without owning a PC or incurring cost from a dealership?
I think the only way you can do it yourself is by downloading it to a USB stick.
Thus requiring a PC or Mac.
If it has older IVI system then update is only possible trough USB Stick by downloading DS Update application on Your PC and preparing USB from that application.
If You car has new IVI System then updates are only possible online “Over the Air”