Welcome to the QuickBooks Community. I'll ensure to share steps so you're able to delete the opening Inventory Quantity Adjustment entries.
To start with, I suggest going to the Search icon. From there, you'll be able to see all the Inventory Quantity Adjustments you've made and the option to delete them.
Here's how:
Select the Search icon upper right corner.
Click Advanced search.
In the Inventory adjustment account drop-down, select the appropriate account.
Choose Inventory Quantity Adjustment from the All Transactions drop-down.
Select Search.
From the search results, select the adjustment you need to delete.
Click it to expand the inventory quantity adjustment page. Then, hit Delete.