@CarloPH 

Are you able to do Controller backups with the access you do have? 

With some careful tinkering you should be able to setup a temporary software controller in the v5.6 version (or possibly later) on a laptop or vm, which will give you new Admin rights to the new controller instance.  If you can successfully perform a site migration (not controller migration) from the current OC200 to the software controller, you will have re-achieved full admin rights without losing any config.  You can then default and upgrade the OC200 to the latest version (5.13) and then perform a reverse site migration from the software controller back to the OC200.

It all hinges on whether you can get that site to migrate or not.

  @CarloPH 

Then you are probably stuck doing screen grabs of all relevant settings and rebuilding from scratch.  Again, you could leverage a temp software controller on a laptop to test with, without committing fully to wiping the OC200 until you are pretty comfortable you go things right.

Hi @CarloPH,

You have no choice but only reset the Controller. If you can't backup all settings, you need to ask for the Main Administrator account from your colleague otherwise you will lose all settings once you reset the OC200.

  @CarloPH 

So if i wanted to social-engineer this problem here's how I'd start.

At the time the departed employee set this up, they probably weren't planning on leaving, and would have most likely used their corp email for setting up the TPlink cloud account (if ever set up, but honestly, you'd be missing a lot if you didn't). So, I would try to login at omada.tplinkcloud.com with their email address.  If it's there, even if you guess the password wrong, you can click a  reset link which will send an email to that account to reset the password.  So get the email address temporarily re-instated, just long enough to try to recover the password.  Once you do that, you can try to login again with the reset password and see if you have access to your site or sites.