There are two ways in which to update GL Determinations:
1. Manually through the Item Master Data window.
You'll notice the drop-down next to "Set G/L Accounts By" displays the 3 options to choose from.
For more information on the difference between these three, see https://support.orchestrated.com/hc/en-us/articles/115015979228-What-s-the-Difference-Between-Warehouse-Item-Group-and-Item-Level-G-L-Determinations-
2. Through our GL Determination Utility. For more information see http://support.orchestrated.com/hc/en-us/articles/206433038-GL-Determination-Utility