Fetch record using checkboxes (Multiple Values)

Fetch record using checkboxes (Multiple Values)

Currently I have a form i.e (Finance Entry) in which we make Payment or Receipt entries.

One of my another form having the entries of our Customer Outstanding. Form name: Payment Outstanding (eMail_Tool).

In [finance entry form] I have to fetch the value from [Payment Outstanding form], I am able to do so using "Lookup - dropdown" (single entry)

this is script I using in "Lookup - Dropdown" [Update_PO] 

  1. // Variable 
  2. FPO  =  eMail_Tool  [Ticket_No == input.Update_PO];
  3. // 
  4. if (input.Customer_Name  ==  FPO.Cust_Name)
  5. {
  6.     input.PO_Name = FPO.Cust_Name;
  7.     input.Invoice_No = FPO.Invoice_No;
  8.     input.INR_Rs_Receipt = FPO.Overdue_Amount;
  9. }

but the problem is, sometime I have to fetch multiple values. (e.g Multiple Invoice's)
how can I do it using checkbox.