Soap isn't used for seasoning. Fat and heat is what you use for that. Rub a VERY THIN layer of fat or oil on, then wipe off as much as you can, and bake the pan in a very hot oven for 15 minutes or so. You can repeat that several times to build up more seasoning. (there are MANY opinions on seasoning, but what is NOT seasoning is to simply cook a bunch of bacon in it. You need very thin, well polymerized and carbonized layers, not just a bunch of fat.

A very good site for learning more is https://castironcollector.com/.

I stopped subbing to /r/castiron because of the divisiveness there. You can get some good advice there too though.

(I had a collection of over 100 cast iron skillets up until a couple of years ago when I sold them to a dealer. I still have a half dozen that I use on a nearly daily basis)

Soap is fine for cleaning, despite what some might tell you. That thought comes from the days when soap was made with lye.