If the device is a common one for this purpose, not custom-made by the BMS company for themselves, then the source for them (original device manufacturer) may have the information needed to create yourself a computer program to ask for and interpret the data.
If the manufacturer of the BMS (or the device) can't or won't provide the information, and no one else has already done this, you could use one of the devices and a terminal program on a computer fed by the USB-485 cable wired to "sniff" the data stream back and forth from device to BMS, and figure out which parts of the data stream mean what, then experiment by sending some of the commands you find to the BMS and what data you get back. It's a tedious process, one that I've not done for this kind of thing, but others have, so it's possible to do.
Alternately, if the BMS has a standard MCU on it with a documented command set for talking to it over the port, you might be able to use that as a starting point (but my guess is that the software for that stuff is made by the BMS company, so the MCU documentation won't have any info on it).
If this BMS is basically the same, with the same features and communications, as another BMS by some other manufacturer, you might be able to get the info (or software, etc) from that manufacturer and see if this BMS responds to it.
I wish it was simpler than that...but it's pretty much the same problem as controllers and their displays: They use basically the same wiring and hardware connections, and data protocols, but not the same data formats or contents, so they are not all inter-compatible, and there's no single "standard" out there that lets someone communicate with a controller via their own display. People have, however, sniffed the data between a working display/controller setup for all the various things it can show or command, and then taken this to make their own display, or their own software for a display, to work with it.
So you might find some info on how to do this in the various open-source display threads (not sure if it's in there or not, but it's a place to start).