Purchase a new reserve/CMOS battery. Shut down, unplug the system and disconnect the battery from the system board.  Hold the power button for 30 sec.  Remove the old CMOS battery and install the new one, reassemble the system and that should reset the TPM and mainboard to defaults. [URL]
Background: My Inspiron 5379 keyboard needs replacement. Dell no longer manufacture parts but provided a number. I bought a part an attempted replacement. Unfortunately, the part did not match Dells specifications so I needed to reassemble 'as was'. Symptom: When I restarted, BIOS had lost its date and time. After correcting that, Windows booted OK but 'hello face' did not function.  Windows Security reported no TPM (previously TPM 2.0 was functioning OK). tpm.msc reports trusted platform module cnnot be found. Attempts to fix: I entered BIOS. There was no option to switch on TPM nor to switch on Intel trusted module. There is no TPM available in device manager. Bare metal reimage (BMR) failed to correct the issue. Factory resetting the laptop after BMR did correct the issue but BMR after that returned the state to no TPM. I tried reinstalling the latest BIOS update to no avail. My guess at the nature of the problem: Because a full reset corrected the issue and BMR after that restored the problem, my guess is that the issue should be correctable with a software tweak/ driver installation. The question:  I prefer not to have to reinstall and tweak all my programs, which are there following BMR. What do I need to do to recover TPM 2.0?
Inspiron 5379 TPM