Custom fields in the issues web form

I am trying to add some additional fields into the issue module. And I am opening the module in the portal for my users. There is no problem for me to add the additional fields to the the issue form. However, I can see the web form for issues is classified as standard form and I am not able to modify it (it is read only) to show more field on the portal for the users.

What will be a best way to show the additional fields in web form?

@gohyc Hello,

Your ERPNext account is cloud hosted? You can customise issues doctype using Customise Form.