Customize new activity form

i need to customize new activity form
and not found in custom form list
and its not the event form
note: i have modified event but not reflect changes in new activity form
How to customize this form

Clear cache and reload and try to customize it it will appear in the list

Try reload but nothing found related to this pop up form

I think customize form is used to customize the core doctypes like sales invoice, sales order etc. there are restriction on these core types in order to maintain the core functionality uninterrupted. if you are working on custom doctype you go to doctypes and find your custome doctype there and you can customize it directly.

also not found in DocType any thing relative to this dialog pop up ( New Activity )

i think thats bcz its not doctype… perhaps frappe team may better know to answer to this, you might edit it from files on your system it might not be possible to do it from gui.

Thank you for your reply.
and waiting for someone to help me.

Waiting for someone to help me.

Did you make it? If so, can you share how?

No , I forget it
but I think you can do it only by client script (JavaScript)