I want to change my order price I deliver it with 50$ but I want to make it 25$ someone help me please?
You can’t change the price of the order after delivery.
Your only solution is to send cancellation request to the buyer and send them new offer with new price after they accepted cancellation request.
Sir this will not effect my order completion rate?
Yes. If you cancel the order, it will affect your order completion %.
The only other option I can think of (apart from what has already been mentioned by @odal456) that involves you not canceling the completed order is by promising them a discount (equivalent to the difference in amount between the completed order and the new amount the buyer has proposed) on the next order they place with you.
Yes sir this maybe an option. Is their no other proper channel on fiver that we can modify our order?
No. There’s no other option.