Not sure the so called "blue bias pot" is labeled below?

I have checked the manual..But still don't know how to do the adjustment...
The measurement is clear..
……
A digital voltmeter capable of accurate
measurements with 0.1 mVDC resolution
is preferred for accurate adjustment (must
have 3 ½ digit display). Use the plastic
alignment tool provided to make the
adjustment. The measurement points are
yellow and black banana test jacks next to
each output tube. Adjust the ‘bias’ for a
voltage reading of 65mVDC (.065 Volt DC) at
the blue bias pot for one of each output tube
pair as follows, noting the voltage setting
of the larger V number tube in each pair is
slaved to the adjustment setting of its lower
V number companion tube: for example,
adjust V5 for 65mVDC and measure its
companion tube V7 to verify a reading of 57
to 73mVDC. Repeat procedure by adjusting
and measuring V9 to read 65mVDC and verify
V11 reads 57-73mVDC; adjust and measure
V6 to read 65mVDC and verify V8 reads 57-
73mVDC, and finally adjust and measure V10
to read 65mVDC and verify that V12 reads 57-
73 mVDC.

Audio Research manual 有寫

有冇師兄可以分享 如何調偏壓？

Audio Research REF150SE

Thanks!