When I was a kid, we used a hammer, nail set (punch) or beefy nail, and a large threaded nut to do chain work.

Set chain on nut with the pin directly over the nut's hole. Hammer/punch pin out. Nut gives it clearance from garage floor so the pin can come out the other side. Do it very carefully so pin doesn't go all the way out.

To replace pin, set chain on floor w/ pin pointing upwards, holes all lined up (no need for nut). Tap pin into place. Twist chain to free up link.

When the pin went all the way out, it took some finesse to get it started back in.

My granddad probably taught me this or we just figured it out for ourselves, since he was a mechanic and a DIY'er and my dad didn't do anything like this.

I remember when I bought my first chain tool in the 70s. What a great little thing! I still have it and it still works (although I hardly ever use chain tools any more, just to cut to length. I use master links exclusively, feeling the Shimano one-use pins are just a terrible design for casual, unpracticed mechanics.

Old chains had rivets that protruded a little out each side, so there was a little bit of a fudge factor and you could eyeball it, and this technique worked great. New chains have much less tolerance and manufacturer's directions should be followed carefully to make sure the link doesn't separate at a bad time.