Probably the best starting point is to talk to the theme devs and just ask in principle how you might customize that particular bit of text (perhaps they have a filter hook, or perhaps there is some other means of overriding it that they’d recommend).
From there, just let us know what we can do to help (we could offer you a snippet to help detect if the request relates to month view, for instance – basically using tribe_is_month() or another suitable function).
Let us know!