Hi Alyssa, Welcome in Community
Follow these steps:
Open your Task Manager by hitting Ctrl + Shift + Esc, find any processes named Microsoft Teams or Teams Installer, and shut them down completely. Once they are closed, try launching the setup file again, but this time right-click it and select Run as administrator to give it the permissions it needs to finish the job.
Try to delete the team's cache:
Make sure Teams is fully closed, then press the Windows Key + R and type
%appdata%\Microsoft\Teams
into the box. Delete every file and folder you see in that window; don't worry about your messages, as those are stored safely in the cloud and will reappear once you log back in.
If the app is still being stubborn, your best bet is to start from scratch with a fresh installation. Go into your system Settings, navigate to Apps, and uninstall Microsoft Teams along with the Teams Machine-Wide Installer if you see it listed. After that, head over to the official Microsoft website to download the latest version of the installer and run it fresh.
https://www.microsoft.com/zh-cn/microsoft-teams/group-chat-software/
Let me know how it goes
Elvis