To customize your route's optimization, navigate to the "Team>Dispatch Board" tab.
(Note: This will open the "Routes" page by default.)
Below the map, you will see your stops for the day. You can arrange the "Daily Stop List" in the order you want them to be by clicking and dragging, then dropping them in the order you want them to be in.
After arranging the visits to your liking, select the checkbox on the left of the stops you want to optimize.
When you have your visits selected, click the "Optimize/ Save" dropdown button and select "Custom Route Order and Save".
Your page will then reload with your Custom Route Optimization set.