For 1.2 mode:
This TPM update utility can be used to:
1) Update your TPM 1.2 firmware version
2) To switch from TPM 2.0 to TPM 1.2.
TPM 1.2 Utility download page
For 2.0 mode:
1) Update your TPM 2.0 firmware version
2) To switch from TPM 1.2 to TPM 2.0.
TPM 2.0 Utility download page
Can you add the 64-bit versions to this page too if poss? thx :)
Is there a 2.0 to 1.2 downgrade utility/option for the Dell Precision 5520?
I can only find the "Dell TPM 2.0 Firmware Update Utility " at the moment (current version 126.96.36.199, A02 from 21st March 2017)
I'm yet to try if it does 2.0 to 1.2 downgrade as well (I don't have the hardware in front of me at the moment) but I suspect it doesn't as the utilities in your links refer to a "Dell TPM 1.2 Update Utility"