Welcome! This forum has a treasure trove of great info – Scouters helping Scouters! Just a heads up, though - all content, information, and opinions shared on this forum are those of the author, not the BSA.
It is very common for users to have multiple BSA numbers - they can log into my.scouting.org > Click Manage Member ID > one of the BSA # will be there marked PRIMARY > then add the other MID (BSA #) - you want to make the one that is your unit registration PRIMARY - that attaches the MIDs together.