ACF can be used to add custom fields to built is WP features such as posts, taxonomies, menus, etc. ACF cannot be used to existing admin pages of WP or to admin pages of other plugins unless those admin pages fall into one of the types of objects I already mentioned.
It is sometimes possible to add ACF fields to a 3rd party form by using acf_form(). This requires that you are capable of modifying the 3rd party form template to insert the acf form inside of the <form></form> tags created by the other plugin.
I do not know if this is possible with the other plugin. If and how this would be done is a question for the developer of the other plugin.
