How can I solve a blacked out display after connecting to an old TV (having accidentally changed the resolution)?

I have this 2018 MacBook Pro 15" and an old Panasonic TV. I used to connect them with a Belkin port via HDMI, but one day I accidentally changed the TV's resolution in Display Settings (from 720p to 480p) on my mac and everything stopped working. I pressed ESC and the setting was not reset. After unplugging the TV and restarting my mac, the mac worked just fine. When I re-plug my mac back into the TV, everything became extremely laggy (screen refresh rate is like 2 seconds 1 frame). I started the mac in safe mode and plugged the TV back in and the result was the same. I have completely no idea how to solve this. Is there any sort of approach such as using the Terminal command lines (just guessing) to change the display resolution settings for an unconnected and used-before external display to recover my mac from this situation?

PS (just additional info which I don't know if related): I used to make use of the command sudo pmset -a GPUSwitch to change the graphic card settings through Terminal. Currently, this command does not work and the mac seems to be using the independent graphic card all the time.