Thanks for reaching out to the Community, @shdeva1. I'm here to lend a hand. 

When migrating from QuickBooks Desktop (QBDT) to QuickBooks Online (QBO), some data doesn't convert. As for the Inventory, once you import it in QBO, it will ask you to choose a date. It uses the date to recalculate your inventory based on First-In, First-Out calculations. For more details about this, see this article: What to expect when you switch from QuickBooks Desktop to QuickBooks Online.

To get this sorted out, try editing the start date or As of the date of the item so QuickBooks allows you to move the date back when creating the transaction. 

Here's how:

1. Click the Gear icon at the top.
2. Select Products and Services.
3. Look for the inventory item.
4. Click the Edit button.
5. On the Quantity on hand, select Starting value.
6. Click the Got it button.
7. Change the date under As of date.
8. Click Save and close.

However, if the prompt persists that you can't adjust the item's starting date because it doesn't have a starting value transaction associated with it, I suggest creating a new inventory item instead. 

Here's what you'll need to do:

1. Click the Gear icon at the top.
2. Select Products and Services.
3. Tap New.
4. Choose Inventory as the type.
5. Enter the information required. 
6. Make sure to enter the date you start to track the inventory item’s quantity on hand in the As of date* field.
7. Pick Save and close.

For more details on how to track your inventory, see this article: Set up and track your inventory in QuickBooks Online.

Let me know how this turns out or if you have any other questions with QuickBooks. I'll be glad to help you further. Have a great day.