Here is a very good comprehensive step-by-step discussion:
pixelprivacy.com/resources/best-wi-fi-channel/
Mac is listed first, but Windows is well-discussed after, a Linux command-line (!) method is nicely explained afterward, and Android and iPhone afterwards.
The only item I might suggest, is that the 5 GHz band can sometimes produce far better performance, depending on many factors, including the makeup of walls, if and only if both the WAP and all client devices support 5 GHz. I don’t buy or recommend WAPs which do either/or though, just both, and on a client, if I get 4 bars with 5 GHz and 5 bars with 2.4 GHz, I generally see better throughput on the 5 GHz.