The operation of a GPS on AstroArch is the same as with Astroberry. The device must be recognized by the pi with the configuration of the config.txt file then it is managed by the gpsd service.
You must add these two lines to the /boot/config.txt file. Then restart the pi
device_tree_param=spi=on
activate_uart=1
You should find your GPS in the /dev directory which should look like ttyAMA0
Afterward, either the GPS is recognized directly with the default GPSD file, or this file must be modified to hardcode the location of the dev point.
In /etc/default/gpsd modify the DEVICES line with the dev point of your ttyAMAx GPS
DEVICES="/dev/ttyAMA0"
If you have your Astroberry files, look at how they are set up