I'm using the free version of Retool and have only one Database available named Retool. All infos I needed to connect Power BI to it was in the connection URL, but it seems it is not your case.
Hey @gatis89, as @Nicolas_Le_Jeune mentioned, you can find your connection string information for RetoolDB on the Connection tab in the Settings modal, accessed from the dropdown on the Retool Database title. We have some docs on this here.
Are you looking for the DB user password for the veikals_db resource? That looks like one of the preloaded dbs for demo data (ie: onboarding_db), but perhaps renamed by someone in your org? Unfortunately we do not give our connection string information for those dbs, but you are able to connect to the RetoolDB from external sources.