Add custom fields to accounts, map them to your CRM, and use them for CRM Account Discovery in Marketo.
Click Field Management, then New Custom Field.
Click the Object drop-down and select Named Account.
Click the Type drop-down and select a type.
Enter a Name (the API Name will populate automatically) and click Create.
After the field is created, select it from the tree on the right. Click the Field Actions drop-down and select Map to CRM Field.
Select the CRM account field you want to map to and click Save.
Once synced, your new field will appear on the far right in your Discover CRM grid.