Hi,
Thanks for using our plugins.
I can help out get you started on this, but for the most part customizations are beyond the support we can provide.
First check out our themer’s guide:
https://theeventscalendar.com/knowledgebase/themers-guide/
That will show you how to move the templates to your theme to modify. You will want to look at these two templates:
\the-events-calendar\views\month\single-event.php
\the-events-calendar\views\month\tooltip.php
As for what to modify we have a snippet here in another thread that should get your close to what you are looking for:
Add venue to week view tooltip
Let me know if you have any follow up questions.
Thanks