So let me see if I understand you correctly. You are having difficulty getting a password to fill in an app, or a website? But when you change the password it is not automatically filling? Getting the Face ID for LastPass should get you to your vault, and if there is a username and password for the app, it should allow you to select it from there, or like I said, it should ask you if you wish to use LastPass to fill the username and password for the app when you have the keyboard appearing to enter the username and password. Also, many of the apps will allow you to configure Face ID on their own, and you don't have to use LastPass to fill once you have filled it once and selected the settings in the app to use Face ID.
Is the problem you are having just with Zoom, or is there something else? If you change the password in the Vault on your PC, you have to make sure that the vault updates in the LastPass app before you try to use it. Are you able to view your vault on the app on your phone? It should work either way.