This will be different in every browser.
In Firefox, you can go to about:addons and open the extension management page for the Bitwarden Password Manager, where you will be able to set “Allow automatic updates” to “Off”. The Firefox App Store for browser add-ons also has a Version History page where you can download older versions.
You can also download the old version of the extension for all supported browsers directly from Bitwarden’s GitHub repository. However, these extensions are not “signed” (i.e., they are not the versions that are available in the browser app stores), which means that you need to use a process called “side-loading” to install any browser extension that you downloaded directly from GitHub. The process for side-loading differs in different browsers, and many browsers do not allow it. Here are instructions for Edge: