That clarified alot.
I guess the reason I asked you to pop open the cover and have a look inside is I suspect that they are using a jkbms or similar Asian generic brand. And the reason they aren’t very forthcoming about it is so that the obscurity factor of their cheap systems remain sort of hidden.
If they are indeed using one of those generic Asian BMS boards, I’d be very very very careful about using those batteries and if I were you, I’d return them.
But should you want to continue, I believe the app you are looking for is XiaoXiangElectric. Where most other BMS apps for Asian brands are rebranded from this company.
There does appear to be an app that you can just download with a simple search for “dyness app”. It links directly to their website and the apps store or iOS pages
Maybe post a picture of the Bluetooth dongle. As if it what I think it is I can with 99.99% assure you that that is what we are looking at.