...
You would send a GET request to the following address (substitute the address of your Okapi instance in):
{{okapiinstance}}/check-in-storage/check-ins?query=(itemStatusPriorToCheckIn=="Available")
If you don't have a reporting tool, you might want to then work on getting that data into a format that can be parsed in Excel. See Use Postman Visualizer to get JSON into a format for Excel for more information on how you could do that.