Unfortunately, there are no settings in the back end that allow you apply discounts too all products in your store at once.

Without having to change the prices manually on every product through shopify (that would take so long especially if you have a large catalog) or purchasing apps to allow the change easily.

We’ve found a FREE solution –

Log in as your store admin
Click Products
Click Export
Select All products
Export as: CSV for Excel, Numbers, or other spreadsheet programs
Click Export Products
Your browser will then download a products_export.csv file
Open the .csv file
Cut and paste all your current prices to Compare at Price field (or leave as they are)
Change all your prices in the Variant Price to your new price
If you’re using Microsoft Excel, enter your new price in the field and move your cursor to the lower-right corner so that it turns into a plus sign (+) and drag the fill handle down and when you let go, the formula gets automatically filled to the other cells
Save the .csv file once complete
Go back to your Shopify store and click Import
Choose the .csv you’ve just edited
Tick Replace any current products that have the same handle. Existing values will be used for any missing columns
Click Upload File
You will see the updated changes.
Click Start import
All products will now be imported with new prices

If you don’t have a Shopify store click here to start and take advantage of their 14 day trial.

Feel free to Contact us here if you need any assistance