Good news: this pump is the correct part for the Samsung front loader WF438AAR. Bad news: the instructional video was inaccurate in every possible way.
On this washer, the pump is located at the front of the machine, not the back. Removing the rear cover doesn't help. What you must do is take off the top, then the electronic control panel, then the door (which means removing the rubber seal, lock and switch), and then the entire front cover of the machine.
After that, you will see the Drain Pump, at the front left corner. Unfortunately, the pump is not held in place by the assembly shown in the video. It's a completely different set of parts that you'll just have to work your way through. The plastic cover surrounding the pump is difficult. It's fragile, and does not want to let the old pump out, or let the new pump in. Suggestion: cut the black plastic flanges that hold the old pump together, so you can slide it out in two pieces. Then slide in the new pump (leave it in one piece, of course) really carefully. It's not easy. I had to tap it repeatedly, carefully, to get the pump to fully seat over the two plastic flanges at the bottom of the cover. It finally seated, but even working carefully, I chipped a little plastic off the end. The plastic cover is fragile to the point of being flimsy. My little chips were Inconsequential, but a structural break in the cover would require ordering a new one, and then waiting for it to arrive. That would have been a nightmare.
The entire integrated assembly you'll be working on (the drain pump is about half of a larger, integrated part) is held to the floor of the washer by a rubber gasket. You can't see it. But it's about one square inch of rubber at the bottom center of the assembly. To get that assembly up and out, so you can access the screws securing the drain pump, you'll need to push the entire assembly smoothly back to the rear of the washer before you start working on it. It'll slide about an inch or so back, and then lift up and out.
You have to take apart so much of the machine, and move / stress so many harnesses and wires, that I thought a working washer was an unlikely outcome. But it all worked, and the machine works great. FYI, when my pump failed, I got no error codes other than repeated "unbalanced load" during a spin cycle that couldn't seem to get started. I could hear enough water sloshing around as it tried to spin that I figured the drain pump must be failing. Ours was about 10 years old.