see here https://wordpress.org/plugins/youtube-channel-gallery/
what you need to change in the shortcode below is just the user=”THISBIT” code from the youtube URL … www.youtube.com/playlist?list=PLrm1v2mWy3sEdd3164inATJW98XQvjLF5
Did you added your own Google API key? Look at the help.
Check in YouTube if the id PLrm1v2mWy3sEdd3164inATJW98XQvjLF5 belongs to a playlist. Check the FAQ of the plugin or send error messages to support.