You can select the frame with the Selection tool or place an insertion point inside it with the Type tool.
Click Fill With Placeholder Text in the Quick Actions section of the Properties panel. You may have to scroll to locate it.
To remove or replace placeholder text, double-click any frame in the thread, choose Edit > Select All, and then delete the text.
Now you can format the dummy text to resemble the final text and present your design-in-progress confidently for client review.