Lattitude 5480 TPM Firmware Upgrade Fails 1.2 -> 2.0 - can't deactivate ownership but why?

Hi, 

I am trying to upgrade the TPM from 1.2 to 2.0 with the firmware patch/release from dell but get the error message. "The TPM is owned. Please clear the TPM and try again"

 

I found this article on how to do it: 

TPM is Unable to Change Between 1.2 or 2.0 Because TPM is Owned | Dell Deutschland

following the first part gives me a different screen which I attached to this post

This already looks different than the screenshot in the link from above. The middle part of the step by step is not applicable as I am not using Dell Data Protection to my knowledge and I couldn't find the mentioned processes either: 

 

 

 

Checking the TPM status shows:

 

 

It seems Win10 still owns the TPM and prevents the firmware upgrade. Any ideas what to do to overcome the issue? 

 

Thanks for your help!