A repeating group is a list. So you will probably need to do a “Schedule API workflow on a list” and then have an API Workflow that creates the new thing.
Just out of interest is this done for billing reasons to get people to upgrade because this doesn’t make much sense as a way to save a list to a database. I have a paying plan so its fine it just feels like a weird way to do things!
Bubble doesn’t like “loops” unless it can be sure how many times you are wanting to do something.
So “Do xxxxxx until you get to the end of this list” … might seem like a good idea until someone codes it wrong and it does it eleventy billion times shutting everyone else out of the system because we are mostly all on a shared bit of kit.
But yes, it is a bit odd at first You do get used to this way of working.
The traditional way to do it is to have two data types - Stock Items and Stock Takes, and the table/data type in between, i.e. Stock Items on Orders, where you put the quantities.
But the way @Simon organized the data, the event “Input element changed” could do the trick, with the proper contitions and action to add or change things. The event is fired whenever a user leaves the input box, and you can grab the “current RG cell”.