Mobile:
Go to Work Orders tab
Select Work Order to edit Cost
Click Time Overview
Select Time Entry to edit Cost
Select Edit
Click Next to get to Editing Time Entry field
Edit Cost in Hourly Rate (Optional) field
Click Done in top right corner
Web:
Go to Work Orders tab
Select Work Order to edit Cost
Click Time Overview
Select Time Entry to edit Cost
Edit Cost in Hourly Rate (Optional) field.
Click Update in top right corner