If you need to import the prices separately, or to update prices in an existing price list, you need to enter the LineNum field in the ITM1 template. This is an integer version of the price list number, starting at zero.
In this case, you need to choose the option in DTW to update existing data, since you will be updating the item object.
If you update a price list that is based on another price list, the manual checkbox will be set and the price will not be updated if the base price subsequently changes.
Note that you can also import and update price lists using the Import from Excel utility in SAP Business One. You can find information on this utility in a companion course.