If you kept backups, you restore the backup. If you have recovery media, you use that. If you have a machine from Dell, Acer and others you see how much recovery media costs. If none of this applies you buy W7 from Newegg, and install.
There's nothing magical here. And most of the time costs a hundred to go back. At the office we moved to W10 entirely and won't be going back.
Odd scenario here- got an older tower that I *think* had Win 7 on it before it was wiped & given Win 10. Wanna go back to 7 but the option is long gone from the Recovery.
What can I do & how?