Sorry poorly written english on my phone (as I’m doing now)
Create a connection, select SQLite (it will probably ask you to download a connector, single button click will do so), then select the file (it’s as you said, the data.db).
Once you finish the connection wizard you’ll see it in the left menu, from there you can expand the tree to see the tables. Double click on the strapi_administrators one, select the data tab, select the row and at the bottom there is an option to delete the row. Then on the bottom right hit save.
(Fair warning I’m giving these instructions from memory, worst case a quick youtube search for DBeaver and SQLite should solve any questions).