What is the procedure for replacing the screen?

It does pretty much snap on, but there are some considerations you may want to take into account. First of all, before you start reattaching the display cables, you will want to follow the display adhesive replacement guide to clean the adhesive from the phone and the screen.

iPhone Display Adhesive Replacement - iFixit Repair Guide

This may not be specific to your phone, but the principles are the same for all iPhones. Take your time and clean it carefully; the better a job you do the greater the chances it'll be sealed tightly against water, dust and everything else.

One note that I found out the hard way is that it's not a bad idea to have more than one sheet of adhesive. The thing is, it's not forgiving in the slightest; if you don't get it on right the first time you don't get a second chance - all you'll end up with is a tangled ball of glue so having a spare on hand lets you put it together permanently instead of temporarily until you can reorder the adhesive sheet.

Most of the time you have to remove the protective sheet from the glue once it's on the phone frame, but occasionally you find one that has a thin line of protective material all around the edge that can be left on while you reconnect everything. For those you take the last layer of protection off just before you place the screen back on the phone. Otherwise you just have to work carefully around the exposed glue and make sure you don't get stuck on it and pull it off.

Once everything is plugged back in, the covers reinstalled and you're ready for the screen, before you press it down do one last test of the phone. Power it up and test. You'll want to check the battery health, verify the screen looks good, make sure the touch screen works and confirm the home button and Touch ID works. Those are the main things to look at in a battery replacement, but if anything else was unplugged or affected during your surgery then you'll want to check that too - for example if part of the procedure is to disconnect the camera, then you definitely want to make sure the camera works as well.

Okay, so now you're happy with the job and all ready to reassemble. Start at the top of the phone; it usually starts a couple of millimeters down then slides up as you flatten the screen down to the phone frame. Click everything in place and verify that the screen is sitting down evenly all the way around. Once it is, put in the Pentalobe screws and you're just about there.

You know how heating the screen softens the adhesive making it easier to remove the screen? Well, I suggest heating it again to soften it when you're reassembling it to help seal it. This is up to you, but I use a hair dryer on the edges of the screen for about three minutes after clipping it back on, then turn it face down and place some weight on it; I use a motorcycle battery myself. A half hour should be more than sufficient, but when possible I just leave it there overnight.

That should give you everything I can think of; feel free to ask if you have any questions.