One will need to locate the white multi connector with ten , eleven or sometimes even twelve thin wires and disconect it ( the connector can be quite tight but will come away). One then needs to probe the wire out put of each pin out on the multi connector.
The easiest method I use to prevent accidentental shorting of pins and meter probes is to use a pair of arduino breadboard jumper wires (male to male).
Often the first wire is black on the multi connector and the last red, other wise the BMS should be marked B-/0 for the black one and B1 - B10 for the other ten positives.
If there are eleven thin sense wires on the connector follow the process below.
# Cell grp one.
Jumper wire one's end is pushed in to the first pin out B-/0 and the second jumper in to the the next pin B1+. Touch each jumper end with the meter probes to log the down the voltage reading (ones hopes it is 2.5v - 4.2v) with the meter dial set to DC 20v.
#Cell grp two.
Move both jumpers along one pin out . Move B1+ jumper into B2+ pin out and B-/0 into the vacated B1+ pin out, perform the same action for a voltage reading.
#Cell grp three.
Move both jumpers along one pin out again . Move B2+ jumper into B3+ pin out and B1+ in to the vactaed B2+ pin out , perform the same action for a voltage reading .
One needs ten seperate cell group voltage readings so one has to continue the same process seven more times .
Once done present the results to the forum here so we can see the readings.