Additional features, settings, or issues not covered by specific Microsoft Teams categories
Hello Samantha,
Thanks for your post here.
When we download the transcript, a .vtt caption file will de downloaded. As far as I know, we can open and edit a VTT file using a text editor, such as NotePad. So you can try dragging the file to Notepad to see if you can open it. If you are using Windows 10 to open the VVT file, to create an association in the Default Apps Settings page, here is an article for your reference: Change default programs in Windows 10.
If you need more help, please feel free to let me know.
Regards,
Seven