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_PriceLevelBase_{level} 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, to update it add a column called Custom_PriceLevelBase_Wholesale. Make sure the price level name matches exactly.