The method to create store credits in Heartland Retail is to return items to a gift card. You can run a report that breaks down your open gift card balances by gift card # in our reporting system.
To do that, navigate to the Reporting > Analysis page. Just add "Gift Card > Gift Card #" on the Groups tab and "Gift Card > ending Balance" on the Metrics tab and change the date range on the Filters tab to "Today." Also, you'll want to remove any other metrics and groups from the report so that only the two listed above have been added.
This is how your report will look like: