Only orders that are not filled and are still in live status can be edited.
Tap on Order Manager on the app screen as shown below.
Locate the order you want to edit in the Orders Manager screen by tapping the drop-down list, sorting by funding currency.
You can edit the price or quantity by tapping the "Edit"
After you have completed the "Edit Price" or "Edit Quantity" tap the "Save & Apply".
Tap Yes to confirm or No, go back to the "Edit Price" or "Edit Quantity" screen