1) Mileage rate has to be updated on individual user profiles under Masters-> edit user -> click on mileage rate link
Enter the rate and date range for which that rate will be applicable then click on Add button.
2) Also, make sure a unit of mileage is Miles or KMS based on whether the user is in the US or another country on the user profile
3) When the mileage rate has to be changed for all users, you can write to support@gorillaexpense.com to let us know about the same. And we will do it for you!
If you do not already have a mileage expense type, you will have to create one by going to Masters -> expense type -> create -> select category as mileage, enter expense type and code. Finally, enter alternate amount label as "distance" and alternate rate as "mileage rate". Make sure the enable multiplier is NOT checked. Once saved, when you login as a user and select this expense type, the mileage rate will be pulled from your user profile and populated