//Get the Supplier Account & Supplier Contact Field Objects
const supplierAccountField = ZDK.Page.getField('Supplier_Account');
const supplierContactField = ZDK.Page.getField('Supplier_Contact');
//Check the Supplier Account Field is not empty
if (supplierAccountField.getValue()) {
    //Get the Name of the Supplier Account
    const supplierAccountName = supplierAccountField.getValue().name;
    //Add criteria to filter the lookup field
    supplierContactField.setCriteria("(Account_Name:equals:" + supplierAccountName + ")", {filterOnSearch: true});
}