Here's the step-by-step process to correct the issue:

1. Identify the correct product for lot "lot a": Determine the product that should be associated with lot "lot a". This might involve reviewing product documentation, checking inventory records, or consulting with relevant personnel.
2. Access the lot profile: Go to the "Lots" menu in the Odoo inventory module. Search for and open the lot profile for "lot a".
3. Modify the product association: In the lot profile, locate the "Product" field. Change the selected product to the correct product that matches lot "lot a".
4. Save the changes: Click the "Save" button to update the product association for lot "lot a".
5. Verify the product association: After saving, go back to the lot profile and ensure that the "Product" field now displays the correct product for lot "lot a".
6. Perform the adjustment: Once the product association is corrected, you should be able to zero out the on-hand quantity of lot "lot a" through an adjustment without encountering the incompatibility error.

By following these steps, you should be able to rectify the product association of lot "lot a" and accurately manage the stock levels for Product "A" in Odoo.