There are two methods of doing this, one where the route is added to the part (shown here), and the other where the part is added to the route

Navigate to Data⇒Production⇒Part

Double click on the part number that is to have the route added, select the Route tab and click New

Enter the route number to be added, or click the search button and double click on the required route from the pop-up window

Enter (or if necessary, amend) the material spec and the production lead time for this part/route combination and then click Save followed by Clear

The route now appears in the list of routes associated with this part number

Click Save