How to make changes in User doctype

I want add some more fields in my User doctype. then i can do the process while creating a user. but when try to customize the User doctype it says the core doctype cannot be customized. So i want to know is there any way to make the process without editing Core doctypes.
My objective : i want to add some more fields while creating a user. for the specific role user manager.

Please check the reference: I unable to Customize User Core Doctype - #2 by NCP

Im already in developer mode, but still i cant save the edited form.

You can see there is no save option.

Because you opened the customize form, not a doctype. Core doctype can’t customize from customize form. that for, you have to update the in the doctype.

If you want to add a custom field to a core doctype without customizing the core doctype itself, you will need to create a custom app and then add the custom field using code. Check out the default HRMS app concept, which added a custom field to the core doctype or normal doctype, and see how it works: How to edit core doctypes like DocType or User? - #2 by NCP

Can i use already created custom app for this case or i want to use hrms for this process.

You can use your custom own app.

Is there any video reference for this process. because i dont understand this process How to edit core doctypes like DocType or User? - #2 by NCP since here used hrms, i dont know where should i add the code inside my custom app’s which module or doctype or i want to create a new custom something.

No … !