I'd be extremely wary (as in run far away) about attempting to adjust the
AFM tension spring.

However, by improvising a flow bench using a shop vac, throttle body, and a
second good AFM, you can easily adjust the spring to match the good one.
Here's an image showing three AFMs in series -- I was adjusting the 1.9l
one which had been breathed on by idjits, and it was easy enough to set it
to read ten percent higher than the 2.1l ones with equal flow.

Yrs,
d