Automatically update bundle inventory
Simple Bundles use the lowest product inventory quantities to keep the bundle inventory quantity in sync. To enable automatic bundle inventory updates based on their product inventory quantities, make sure Enable automatic inventory sync for bundle quantities is enabled in your preferences.
You also need to ensure that Track quantity is enabled on your bundle variant in Shopify.
We also recommend unchecking Continue selling when out of stock to avoid negative inventories and bundles going into negatives.
Automatically trigger inventory sync for all bundles
If you've updated products in a bundle or changed inventory settings in Shopify, your inventory quantities may go out of sync. In this case, you can manually trigger a sync across all of your bundles, by going into your Preferences page, navigating to the Bundle inventory section, and clicking on Resync all bundle quantities.
Note: All parent bundle SKUs should be tracked bundle inventory management to Shopify so that inventory can be adjusted properly. How to check this? You could export your bundles and check in the inventory_management column. Here's a guide to bulk exporting your bundles. (https://help.simplebundles.io/article/103-bulk-exporting-bundle-data).