Automatic transmissions contain a lot of complex parts that have to be removed and installed correctly with precision in order for the transmission to work correctly once rebuilt.
I once tried my hand at rebuilding an automatic transmission before because it was winter and I had nothing else to do so I tinkered in my shop and decided to try it to see if I could rebuild it.
I got the transmission back together after 3 months and then put the transmission back into my truck and it didn't work.
So I took the truck to a transmission shop and told them that I rebuilt it and it was working fine after they did the rebuild.
Not sure what they did but I know I messed the transmission up somehow.
You could likely learn it but probably not from a video.
If you're not sure what you're doing or have never rebuilt an automatic transmission before then it's best to leave the rebuild to a transmission rebuilding pro and transmission rebuild shop.