I can't provide detailed information because I have no experience with embedded ECM in BAW. My experience is with external CPE and ICN only (i.e. configuring BAW with a pre-existing FileNet P8 system).
But I would start with running BPMConfig -export to export the current configuration to a folder.
Then consulting the sample configuration file most closely matching your existing BAW config under AppServer\BPM\samples\config, finding the relevant DosDb (and maybe TosDb) section. Add these with real values to the the config file you exported (probably De1.properties).
Then run BPMConfig -create to (hopefully) create the design object store database.
That's just my guess. But see https://www.ibm.com/docs/en/baw/24.0.x?topic=components-configuring-your-system-case-management for info.
I don't know whether BPMConfig will go on to create the object store, or if you have to use ACCE to do it after the fact..( as I said I've never used or built BAW with the embedded ECM option)