Take a quick look at your battery. What you have in hand is the adapter cable. Plug it directly into the left male connector and plug it into the B6 to charge. a flat cable, because yours is 3S, so there should be one with 4 wires. Just look for it, plug it into B6 and that's it.
If the capacity and state of the four batteries are the same. similarly, they can be numbered 1, respectively. 2,3,4 are connected in series, then press ▲1▲2▲3▲4▲ to connect. ▲This is the wiring point, that is, four batteries are connected to five wires. You can purchase a model-specific balancing charger. Equivalent to the 4S battery used in the models.