How to make a field disable and set a value in the disable field based on other input filed

Hello Experts,

I have a requirment where on  a view one field is F4 field and other is Dropdown input field.

If user is selecting some value using the F4 type field then that dropdown type field should be filled

with some default value and it should be in disable mode.

Please suggest me how to proceed in this case.

Kind Regards,

Sudarshan