First, Export the product list. It is recommended you only keep the products you want to update and remove the rest from the exported list.

Add a column to the file named Custom_PriceLevelUnit_{level}_{unit} and set the price you want. You can set the price as -1 if you want to unset the overridden price.

Eg: If you have a Price Level called Wholesale and a unit called kg, to update it add a column called Custom_PriceLevelUnit_Wholesale_case. Make sure the price level name matches exactly.

After making the changes, Goto "Bulk Update Products" and upload the excel.