Here is a simple way to have a useful loop over collections or tables. It is great for many admin tasks and simpler than writing a custom action.

Create two page state variables (or app state): loopCounter and loopMax, both integers.

create a button on the page and an (optional) progress widget:

create actions for the button like:

The logic is simple:

read the documents of the collection/table. give the output variable name a meaningful name
set loopCounter to 0 and loopMax to the number of documents/rows
loop while loopCounter < number of documents/rows
1. perform whatever action you need on the document/row (i.e. set field). get the document reference by index of loopCounter (see below)
2. increment loopCounter
3. a short delay (optional)

in the progress widget,
conditional display: loopMax > 0
progress value: set ctr and max variables from the page state and use code expression: (ctr / max).toDouble()
text: set ctr and max as above and use code expression: (ctr / max * 100).toInt().toString()+\"%\"

It works great for me on small dataset. I'm not sure if it will work on big/huge collections/rows as maybe FF tries to load them all in memory

How to loop through Dataset or Table control?