YouTube. Like, a year ago. Um … rather late in life. That comes from doing very little cycling when I was a child (my parents live on a narrow windy busy road, and even now I consider it rather scary to ride), and then doing almost all of my cycling as an adult in Asia - and getting repairs done for near-free at bike shops.
So, yeah, YouTube lessons. And it’s a bit like cooking a new recipe. The first time you do it, it’ll take forever, but then it gets much faster after that.
Not that you should be taking any lessons from me. I changed my back tire a couple of weeks ago, and it’s great for rides, holds pressure and all that and is at the same pressure when I get home as when I left, but now for the second time it’s deflated to nothing at home over the next day or two. I pump it up, and it’s fine.
A while back I asked here if anyone was willing to teach me, and a couple of people provided very encouraging replies, but I never followed through on it. That may have been because it was summer and I try to avoid being outside after 9am.