long story short:

• I have a good working iMac 2015 5K that I wanted to sell.
• I cannot do an automated factory reset on this device, so I had to go through steps.
• I accidentally wiped a wrong disk, at least I think I did.
• After wiping I get the folder/questionmark at startup.
• I restart with COMMAND + R - To get a WIFI list to choose from, I connect and download certain recourses.
• It reboots in a menu where you can go back to CAPITAN X. But when it asks on which disk I want to install, there is nothing. I cannot continue.
• I did the first AID on all 3 given disks (HDD / SD and recovery) and it showed green, no faults.

What should I do? Apple wanted to ship me off to a dealer, which costs me money. I known I did something 'wrong' but I need to get an OS back on my iMac. Any help is much appreciated. Ill send a pizza!

thanks, Jeroen The Netherlands.