PHP code to subscribe user without commenting

Hi Guys
I have a bit of custom PHP code where my users can sign up for events. What I’m looking for is whether there is a piece of PHP code I can use to automatically subscribe users to future comments when they press the “sign up button”. Also if possible code to un-subscribe them should they change their mind and not participate in the event.

Hope my question makes sense.

Thanks
Jacob Thastrup

https://ww.wp.xz.cn/plugins/subscribe-to-comments-reloaded/