Adding custom fields to a template's custom post type

Hello,

I am using ZeeBizCard theme (https://themezee.com/zeebizzcard/) for my wordpress site. This theme added a new custom post type named ‘portfolio’.

I am also using the TF Social Share button plugin for my site.

Long story made short, I need to add the custom field “disable_social_share” with value “yes” in my ‘portfolio’ custom post types to disable the social share button in selected ‘portfolio’ posts.

Since the custom field box doesn’t exist in the ‘portfolio’ custom post type (not a ‘screen options’ problem), I figured I need to put a code that calls the custom field box somewhere in my theme files. Anyone could help me with this?

Or, any other alternatives which enables me to put “disable_social_share” with value “yes” in selected posts will do.

Thank you in advance, any help would be greatly appreciated ??