You actually need two functions under Administration --> Workspace: AutoField and Service Level Management.
AutoField only works on dropdown fields. It allows you to configure one dropdown field (Result) based on multiple decision (dropdown) fields.
The Service Level Management function configures the calculation of SLA Response Time and SLA Due Date based on the configured Result field.
For example, you have a dropdown field for Country and the built-in Priority. You may have different service levels for each country. You would create a new dropdown field called Service Level that contains the various service levels used in all countries. You would configure AutoField to calculate Service Level based on Country and Priority. Finally you would configure Service Level Management to use the Service Level dropdown field.
Feel free to drop some more details about your configuration if you need more help.
You need to use AutoField to set the value of the SLA dropdown field, which will then set the values of the SLA date fields. Let’s say you have 2 fields that contribute Priority and Department, Priority has possible values High, Medium, and Low and department has Possible values Sales, Marketing, and HR. Your SLA dropdown field should have values: High_Sales, Medium_Sales, Low_Sales, High_Marketing, Medium_Marketing, Low_Marketing, High_HR, Medium_HR, and Low_HR. Then setup the Response and Resolution times for each of those 9 SLAs. Then use Autofield to set the SLA field based on Priority and Department. You will be able to get away with less than 9 choices if some of them have the same Response and Resolution times, but the 9 would be better for reporting purposes if necessary.