In that case, please follow the three steps I had outlined in my comment above, and take screenshots at each step (e.g., by using the keyboard shortcut Alt+PrintScreen). Post any screenshots that look significantly different from those that I had shown (but make sure to redact any personal information visible in the screenshots before posting).
This statement indicates that you are not actually accessing the Bitwarden browser extension, but that you are instead opening the Bitwarden Web Vault (accessed via the website vault.bitwarden.com). The Bitwarden Web Vault is the only place where the master password can be changed.
To access the browser extension, you must click the puzzle piece icon (
) to the right of your browser address bar (see orange circle in the screenshot below), and then select “Bitwarden Password Manager”:
P.S. If you click the pushpin icon (
) next to “Bitwarden Password Manager” in the Extensions pop-up menu (accessed via ), then your browser will get a pinned Bitwarden shield icon (
) next to the address bar, and you will be able to directly access the browser extension by clicking on the shield icon.