it should just go away by viewing the chat of the missed call. If that doesn't show up do you recall who the call was from, you might have to start a new chat with that person for the message to get marked unread.
Also check Teams.microsoft.com see if it shows there as well, if not then could be a cache issue we need to address.
Best Response confirmed by
C Edwards (Contributor)
This icon has been showing on this channel for me for ages. I can't go back and find where I missed it, or who it was from. There needs to be a way to remove it that is more direct. It's annoying that a UI would yell at me about something that is obviously no longer relevant. Clicking the icon should take you to the chat you missed. Or should have some action to allow you to clear notifications. Or even have a tooltip to tell you what it MEANS. It's been on my teams view for months. I just now figured out what it meant.