I think it's a bit of a question for you how you would like the logistics of revealing hidden sections to work, but here is one idea.
I assume you already have something like this:
- A field in the repeating group called Hidden
- A button that sets Hidden = true
- Conditional formatting on the repeating section with the condition Hidden = true -> Hide
How about adding this to your form
- Add a boolean field outside the repeating group called ShowAll, and show this as a checkbox in your form. Have it default to false
- Modify the conditional formatting on the repeating section to condition: Hidden = true AND ShowAll != true -> Hide (here != means "is not equal to")
- Add a new button in the repeating section that sets Hidden = false
- Hide the Hide button when Hidden = true and hide the Show button when Hidden != true
This should provide you a way to show all the hidden sections, and mark them as un-hidden if you need to.