It is not possible to edit the entered weight. If you entered a weight that is too low, the growth is probably more than expected. If you entered a weight that is too high, the growth is probably less than expected.
When you entered a wrong average weight, it is advised to remove the supplied animals and supply the same animals again, with the correct weight:
Go to Farm.
Select the Location.
Click Remove.
Click Ok.
Click Supply.
Enter all details and Click Submit.