Using headphone port as audio input on 2019 MacBook Pro Sequoia 15.1

Hello all. I have googled this question but the info doesn't seem to be correct. I have read (and see a YouTube video) where the standard headphone output jack on a 2019 MacBook Pro could be used as input jack by going into the settings, clicking on sound, scrolling down to the input/output and then clicking on output to change the port setting to input. I need to quickly record something from an external microphone and I don't have a digital audio interface. It needs to be an external microphone - the built in one isn't an option. Can anyone talk me through the steps (if I'm not imagining it all).

Many thanks