How can I group our customers according to the first two digits of the zip code?

You do not want to group your customer by zip code (ZIP), but only by its first two digits? Proceed as follows:

1. Create a custom field for customers at Options > Custom fields > Customers, e.g. '2-digit ZIP' (see Custom fields overview).
2. Export the customers as an Excel file at Customers > More > Export (see Export customers).
3. Add a new column to the Excel file for the '2-digit ZIP' field. Fill this with the first 2 digits of the ZIP code, e.g. using the LEFT formula (for details, see the Microsoft support article LEFT function):
   
4. Reimport the customer data. To do this, only assign the '2-digit ZIP' field and the key field. In this way, only the '2-digit ZIP' field is updated (see Update customers).
5. In the territory optimization, go to Optimization settings > Grouping.
6. Click on the pencil icon. A pop-up window opens.
7. In the selection menu, select By custom field and then the field you have created 2-digit ZIP. Save.
8. Click on Start optimization to initiate a territory optimization.

During the territory optimization, customers of a group (i.e. the same first two zip code digits) are now only assigned together to an area.