Make sure that the Tax to be updated is added first. To know how to add a Tax, please click on the below links

    Add new Tax Type

   Add new Tax Group

1. Click Products on the Navigation bar and select Products from the drop-down

2. Select the Product and click on edit

3. Scroll to the Price field, click on Tax and select the Tax to be updated for the product


4.  Click on Save to update the changes made