iMac OS Reinstall - Permission denied

Hello!

I've got a new iMac for work and I did the mistake to log-in with my personal apple ID and it started copying all my personal data, while I only wanted work related files on this device. That is why I've decided to find a way to somehow reinstall my OS and take it to it's factory settings.

I've found this OPTION+COMMAND+R holding method while restarting. At first, I've got an error on that screen where the globe is spinning. I've somehow managed to get over that and now if I am trying to reinstall the OS I am getting a "The operation couldn't be completed. Permission denied". No matter what I do, I end up back on this screen and I can't do anything from here.

I am not a programmer or a OS expert. Anybody having any solution for this?

Thanks in advance!