You may be able to force your BMS to balance your cell groups by leaving your charger plugged in for a few hours after the charger light turns green.
You would need to trust your BMS to NOT charge any cell group past 4.21 volts.
I think Das-Kit is pretty good with using safe BMS's that will not overcharge the battery, but I'm not positive.
If your owners manual mentions that you should unplug your charger after a certain amount of time and leaving it plugged in for a while after the light turns green is OK, then you should be OK to try and balance the cells.
My owners manual (for my Das-Kit powered Et.Cycle T1000) says that the battery is fully charged after 7 hours but should be unplugged within 14 hours.
I don't want to give any bad or even dangerous advice, so if
@harryS or anyone else thinks that this is a bad idea, then please say so.
I would suggest doing a long charge with the battery and charger in the safest place you can find, where a fire won't burn down your home.
This is a good video with a lot of common sense,..