Comment Form Text plugin

Hi,

I want to use the Comment Form Text plugin, https://wpmudev.com/project/comment-form-text, but am having problems with it.

It does not show anything, probably because I have to add something to my theme somewhere, but I have no idea what or where.

Please let me know what and where I have to change things in order for this plugin to work with my theme which is NOT downloaded from here.

Thanks,

Paul