I bought a used fortigate 100E. How can I deregister the previous owner?

Hi ​@sagelike18 ,

You can reach out to Fortinet Customer service team to deregister the device from the support portal and can register it under your email ID.

You can contact Fortinet Customer Support to assist you with this.

Only thing you can do is to ask Fortinet Support/CS team to contact the current registered owner to release the registration. If the current owner refuses, nothing else you or FTNT can do.
By the way, 100E’s End of Support (EOS) date is 2026-08-17. After that, nothing would matter like who owns/registered it.

Toshi