I have a multiselect field and I would like to retrieve the value from another view based on each multiselect selection and input it another field

View1:

Form:

when user first selects the 1001 in the multiselect field then a script will retrieve the respective "Subs" value from view1 which is 3000 and input it to " Est.Subs-Selected Fips"

and then when user selects next Fips value --1003 -- then the the " Est.Subs-Selected Fips" will be updated to 4000.

Could anyone please help me on script ?

Thanks

Arfater