Trigger price range is just an information display for you. It tells what is the range of price within which you can set your stop loss. Ultimately, the stop loss value has to be decided by you within that range, based on how much you can afford to loose.
Trigger price is your actual Stop Loss price. This will be an empty box, you need to fill the stop loss value here. Stop Loss value is decided by you. If you place a stop loss value outside the trigger price range (info display) your order will not be submitted.
Usually trigger price range varies based on specific stock and it is 1.5% to 3% range, I believe.
Edit:
Since all Cover Orders are market orders, you need to only specify the trigger price which is your stop loss price. You should not modify the value in the trigger price range, it is automatic and just getting displayed only for your information. You need not do anything with that.