they mostly just picked the good ones, thought i can edit some things with dark room effects by adjusting stuff, and combining certain portions of two different photos... (only in black in white though)
I'm sure they edited photos before computers, it just takes more time. My uncle ran a photography studio business before digital age and I would see him working like a painter (easel and all that) sometimes. I suppose a lot of things happen in the dark room too.
Before computers, all photo editing was done in the dark room. There are various different things you can control while printing an image in the dark room including the amount of exposure, cropping, minor color adjustments, minor "cutting and pasting" (literally cutting and pasting from frame to frame), etc. Photoshop can obviously do way more, much easier, and much faster.