Either reduce text amount or extend text frames.
Or reduce text size and/or tracking.
And in future it's best to Place text.
Use the Story Editor to see what is going on. Edit menu - Edit in Story Editor
Then in the Type menu, click "Show Hidden Characters"
All overset text will have a red line on the left and says "Overset" with a line that shows exactly where the text in the frame becomes overset.
You mentioned having a lot of text frames. You may have redundant or repetitive text in more than one frame.
When I have worked on other people's files I have seen numerous whole paragraphs of text overset.
Of course, the question was, is this text supposed to be on the page?
If so, you need to enlarge the text frame or click the red cross (in layout view).
this loads the overset text into your cursor and then you can click and drag a new text frame on the page to show the overset text.
If the overset doesn't need to show on the page, it should be deleted along with empty returns.
If the overset text duplicates some text from another frame, this means that either the text frames aren't linked or are linked incorrectly.
When editing your text you should always check to see that NO frames have a red cross at the bottom right of any frame. (overset text)
Be aware that something a small as a period added at the end of a sentence may cause text to be overset.
Understanding how to use Preflight is really useful in finding overset text (and other issues) in a document.
Thanks for all your replies.