Multiselect - Returning all selected fields

Multiselect - Returning all selected fields

I have two forms. The first form has a lot of information on different contacts. The second form has a multiselect lookup field where a person can select multiple of the contacts from a list. I am trying to write a script where it will them return all of the selected entries and add 1 to one of the fields.

Here is the script I wrote for the same thing except a dropdown box instead of a multiselect: 

dat  =  Add_New_Contact  [First_Name == input.Find_Person];
dat.of_Appointments = (dat.of_Appointments  +  1);

How can I modify this to work for a multiselect (i.e. I can add 1 to multiple entries at once.)

Thanks