After you add last-minute Orders to an optimized plan, they appear as blue markers (unserved Orders) on the map.
At this point you can re-optimize everything, possibly revolutionizing all your Routes, or you can decide to fit in the unserved Orders while keeping the existing Routes and taking advantage only of residual resources.
Full Optimization is the default option which you also choose when clicking on the general Plan Optimal Routes button. It re-optimizes everything.
Fit in unserved Orders preserves the existing Routes and assigns the Order(s) to the Drivers whose schedules still have some availability.
Please note that if you select Fit in unserved Orders, Routes with violations will be ignored by the optimization process.
If all Drivers' Routes are locked (read more about locking routes here) both Full Optimization and Fit in unserved Orders will not be available either.
You can always go ahead and assign the new unserved Order(s) manually, by clicking on the marker and choosing Fit in from the bubble.
Another window appears, asking you where you want to insert the Order. By choosing Best Fit in both fields (see below) you basically ask the Route Planner to decide for you where to insert the Order (same as "Fit in unserved Orders").
Alternatively, you can select a specific Driver from the Select Route drop-down menu and the position in his/her sequence of stops from Insert after.
Please note that in case of violated constraints, the option "Best Fit" is not available and the assignment has to be done manually.