Welcome, @dgold to the community.
Export a CSV from Bitwarden and use that as your starting point. This will give you the exact and current import format, most notably the current header row.
Do note that repeated importing will result in duplicates, so you probably want to purge your vault (on the ‘My Account’ page in the web vault) before the final import.
Also, this counts as a “big change” to your vault. Unless your Bitwarden vault is brand new you might first create a JSON or ZIP backup so that if you royally mess up it can be restored to “yesterday”.