Op, I'm an electrician. This comment is the best advice. All boxes used for fans need to be fan-rated. This is possible to do without attic access.
I haven't watched the video but this looks to be an okay start: https://youtu.be/DKWeyydoYTI
Just remember that ceiling fans are heavy and the little wiggle over time will cause more wear and tear than you might think.
Best of luck!
That's how we know you're a real electrician lol.