Auto fill in fields after selected lookup dropdown menu

Hi everyone~ good evenning/morning

I am a very new and beginner of Zoho creator. i have test almost a week, and created some databases and forms for users.

i am started to love zoho products and i am considering to have paid version instead of trial version.

Currently, i am having a probelm which blocked me a few days, still can not solve it.

simply, i have only 2 forms which named capacity and order

Capacity = is a kind of database that is about product information such product name, size, price.

Order = is the form that user submit the orders

below is form capacity screenshot:

below is the form order screenshot

below is the problem that i am having:

for example, when a user fill in product field with Apple, the field of size will show Small and Large in dropdown menu for user to select. (according to the form capacity)

and i would like to have the price field to update and shows the price according to the user selected.

for example, when user selected small, the price field shows 5, on the other hand, when user selected large, the price field show 10. how should i do? please help, thank you so much.