How to reset El Capitan instead of Sierra or reset iMac Late 2015 to factory settings?

Question

macOS

Hello.
Ran into issues with macOS Sierra and would like to return El Capitan back to iMac Late 2015 , the system that came from the factory. But I ran into a problem. When trying to download El Capitan from iTunes, an error pops up " Your system is too new to install this update ..." and El Capitan cannot be downloaded.
In addition, when rebooting to the system menu via Command + Rthe reinstall system section already shows "Reinstall macOS Sierra" even though it says "Reinstall OS X" from the factory. Maybe there is an opportunity to return this same boot sector to the factory settings so that you can download again automatically and reinstall OS X? But how to do it? I tried to format the disks, it does not help, it is sewn into the motherboard somewhere and I don’t know the commands for the terminal and I can’t formulate a question for Google. Help me please.
It is apparently impossible to find an OS X image in official sources, and there is no desire to download from torrents from incomprehensible sites.

Answer 1

Found a solution. I had to completely format the disk and delete hidden partitions. I made a bootable Windows 10 flash drive and formatted it using the Windows installer.

Answer 2

you can use a flash drive
, you can Shift-Option-Command-R on restart
, in general, I advise you to use a time machine. practical.