Apply custom filter in the lookup of Resco CRM JS Bridge

Hi Resco JS Bridge experts,

I am trying to apply a custom filter on the Lookup in Resco CRM form as it cannot be done using the 'Edit Filter' of the lookup. Any idea how can I apply this?

I tried using the code below but I don't know where should I bind it. It should trigger on click of the lookup field.

var lookupForm = new MobileCRM.UI.LookupForm();
var customXMLView =
    `<fetch version="1.0" output-format="xml-platform" mapping="logical" distinct="true">
        ....</fetch>`;
lookupForm.addEntityFilter("fieldname", customXMLView);
lookupForm.addView("fieldname", "Default", true);
lookupForm.allowNull = true; // Allow choosing empty value

Thank you!