If you need to set several SKUs as non-replenishable and have that information in a spreadsheet, you can bulk upload the information to Inventory Planner.
Create a spreadsheet that has one column with the SKU (or other unique identifier) and one column with the replenishment status. For items to be marked as non-replenishable, enter '1' or 'true' in that column. Your spreadsheet must have column names in the first row.
In Replenishment, click on Upload > Replenishment.
Attach your spreadsheet and choose the appropriate column name for each field. Replenishment status will be noted in the "Hide in replenishment column (optional)" field.