Use this script to convert a number to a list. This is particularly useful when you want to create several new linked records based on a number in the triggering record.
Copy and paste the script in to a scripting action. (You can open the script in a plain text editor.)
Set up the listLength input variable.
Test the script. This will output the list you need to set up the repeating group.
Set up a repeating group using the list output by the script.
Note that Airtable does not guarantee the order in which items in a repeating group run, so there is a chance that records will be created out of order.