The method does exist (as of Rails 6.0.0) for PostgreSQL:
Note that you are using SQLite:
So your available methods are here: https://api.rubyonrails.org/classes/ActiveRecord/ConnectionAdapters/SQLite3Adapter.html
More importantly, YOU SHOULDN’T RESET YOUR TABLE IDS JUST BECAUSE YOU DELETED A USER. The database can handle incrementing the IDs no problem, even after you delete a user.
I’m having a hard time coming up with a use-case that would require resetting the Db Ids after deleting a record.
If you REALLY want to do this: Reset the id field in a table in a sqlite db in Rails
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