Most engines have one O2/AFM (aka wide band O2) per bank, some inline have 2 and some modified engines use one per cylinder which is much better but more expensive and complex.
Given this V6 has one per bank fuel trims will tell which bank or both are adding fuel (eg +10) for a lean condition or taking fuel away (eg-10)because its rich.
If one bank is hovering around 0 give or take a couple of points and the other is +10 for example then that bank is running lean.
The problem is that bank has multiple cylinders making it difficult to pinpoint the exact one if the misfire count is the same for all.
Enriching the whole system through the TB wont help pinpoint the issue, checking the fuel trims to find out what is happening is the only real way to get a good starting point.
Back in the day when engines has secondary air system ports for each cylinder and no OBD 2 we removed them one at a time and put a gas analyzer probe down it to identify the offending cyl.