@craigtest
To change the resolution add to the end of cmdline.txt file the following:

video=HDMI-A-1:"add_your_width"x"add_your_height"M@"add_your_refresh_rate"

Example for 1080p 60HZ resolution:

video=HDMI-A-1:1920x1080M@60

To open the file from a terminal window just type:

sudo nano /boot/firmware/cmdline.txt

To save the change press ctrl+o and ctrl+x and restart the system.