Go to Setup > Customers.

Go to Setup >> Customers.

 Use the available filters to search for the customers for which you want to set up the Days of Service massively.

 Click on Days of Service Mass Update

 The Mass Update Days of Service window will open. Enter the carrier for each day and once you have finished click on Process.

A confirmation window will open informiing the number of customer for which the days of service will be updated. Enter the word Confirm and click on OK.

The Day of Service window will appear. Click on the carrier's name and click on the "Save" button. The carrier name will appear next to the day of the week. A confirmation window will appear at the lower-right corner of the screen.