Hey Jenna,
Oh, gotcha, I see what you mean — thanks for clarifying!
Unfortunately, the Month View tooltip does not accept HTML formatting in excerpts right out of the box. While I haven’t tested it personally, the suggest in this post might do the trick:
https://theeventscalendar.com/the-trouble-with-excerpts/
Hopefully that does it. If not, it will otherwise take some custom development which, unfortunately, is outside what we are able to help do here in the forums, particularly in Pre-Sales.
Cheers,
Geoff