What would be a fastest way to add all my miles instead of one by one if I drive the same distance?

Create one mileage expense and save it to your report. From there you can click on the expense and choose the option to Duplicate the expense. This option could be hiding within the 3 dots to the right of the Delete button. You can make any edits to the duplicated expense (Date, Deductions, Comments, Allocations, etc.) and then save the new duplicated expense.