I brought the Technics SA-R210 receiver from US to Taiwan. How can I change the FREQUENCY STEP from FM/AM 200Khz/10Khz to 50Khz/9Khz to cure the
problem of "No FM stereo" and "No AM"?

It might not be possible without really major surgery... it looks as
if the SA-R210 may have been made specifically for the US and Canadian
markets.

The manual says that in manual-tuning mode, the FM can be stepped
along at a 100 kHz increment. It may be only the "auto-scan" tuning
which insists on stopping only on the odd 100 kHz frequencies.

On some Technics receivers of that era, pressing the "AM" button for
four seconds or more will toggle the tuner between 10kHz and 9 kHz
channels.

You could try a similar long-press on the FM button to see if there's
an undocumented frequency-offset change in the firmware.