Miles to empty

You can’t fix it ,the computer does it

 

You don't fix it. It is just a stupid blind estimate, a forecast that assumes the future driving conditions and MPG will be exactly the same as recent past conditions and MPG, which is almost never true for many of us.

Someone else had a similar question today, here is my response to him:
My how many miles until the flashing light comes on is always different | PriusChat

My guess is that your previous tank had an unusually high MPG due to excellent conditions or a different-than-usual trip. Now you are back to normal driving conditions.

 

On the Nissan Leaf (electric) we call that function the [Guess-O-Meter]. It takes the most recent mileage estimate and projects that onto the current fuel level. As driving conditions change, so will the 'guess'.

If you want it to improve, there are driving methods you can learn to improve it. They are not necessarily easy, and take constant attention.