The dash does not have a trip odometer.
Try writing down your odometer reading when you fill it up.
Drive until almost empty.
Observe odometer reading when you go to fuel up, write it down.
Write down how many gallons you put in.
Subtract last odometer reading from the first one.
Divide miles to gallons used. This will give you mpg.
Report back with your results.
There are online calculators to assist with the subtracting and dividing if needed, but the pen, paper, and effort required to write 3 numbers down will have to come from you.