"You must select an OS to continue" on a Mac already on OS X El Captain

[gontie]

Hello,

I have read a lot on the forum and checked videos on the internet and i cannot download again Yosemite from My MAC which is at version 10.11.13.

What can i do to download again the software to avoid this message ?

Is there any way to proceed to the USB stick creation with the new disk utility ?

I am technician in Windows but Macos is really new for me

Thanks in advance for your help.

 

[Obvious Answer Man]

Nothing.