Hi,
If the fields does not show up in the list when you are searching for them, that means they simply does not exist for sure in the wp_postmeta table. There are multiple reasons that could happen:
1. if the field is not in use yet: no values have been assigned to it on a post/post type object. Once there is at least one post/cpt with a field value it will show up
2. the actual field name is different from the label name
3. the field is not actually a post meta field, but stored in a different table
In case of issue 1. you start using the field, and it should appear sooner or later. With issue 2. you may have to look around or ask the developer if there is a way to get the actual post meta field name. In ACF for example you can see the “slug” field, which is actually the custom field name.
With issue 3. there is nothing we can do unfortunately – if the values are stored extrernally there is no way for the plugin to access them.