iMac recovery or reset not possible with High Sierra

Hi,

I sold an iMac "27 late 2009 with MacOS El Capitan to a friend.

I made the clean up before passing it.

Obviously I made a mistake and didn't follow the Apple instruction properly with the factory reset.

I started the reinstallation process and quit with cmd-Q before the Apple is asking approval for the law text. I thought this is no longer my computer so it is not my job to approve anything anymore.

I passed the imac to a friend and he got stuck with the apple id part. It didn't approve his apple id and therefore he couldn't do anything with the iMac. It gave message "This item is temporarily unavailable. Please try again later"

After two days of googling I found solution and possible reason for this issue. I should have approve the law text and start the installation with my apple ID which was originally used when I bought the iMac and after that I should have quit the installation process with cmd-Q.

OK, so this friend now has fully working iMac and he updated the MacOS to High Sierra. But then he wanted to install SSD and therefore he tested the recovery mode before doing any hard disk installations, and again it doesn't take his apple ID username/password. It says "This item is temporarily unavailable. Please try again later" the same message that he got before. It seems that the recovery is trying to reinstall the El Capitan MacOS which is assosiated with my apple ID and therefore he can't reset the iMac with his apple ID. We have tested several key combinations: Command (⌘)-R, Option-Command-R, Shift-Option-Command-R

So, I am now asking if anyone has any idea why in the heck this iMac is trying to reinstall the old Mac OS instead reinstalling the High Sierra which has been assosiated with his apple ID and currently running on iMac? Basically now he Can't resell this iMac to anyone unless I go there and insert my apple ID. This person lives 125km away, so I am not very keen on driving back and forth just because Apple has made the reselling too difficult.