参加希望の方は、facebookイベントページでgoingをしてくださいって英語でなんて言うの？

The first example is a soft request. The second example uses the word 'registration' which some may believe means that it is necessary to register for the event before attending. The third example is far more prescriptive, and you would worry you may not be admitted if you did not click the icon!

Both of these sentences are more casual ways of asking people to click the going button instead of just clicking the 'interested' button. There are more formal ways to ask, but if it is a Facebook event I'm sure you'd like to keep it loose and casual.

There are various ways of asking one to attend an event Above I have provided two good examples to convey that one is interested in attending an event.
Click and press are synonyms and suggests an act of selecting an option on an electronic device.

The above sentences are the number of ways you can tell someone to click "going" on Facebook to confirm that they will be attending the event. You can also say something like:
-Please click "going" if you would like to attend our event.
-Click "going" to confirm that you will be attending the event.

We would like to invite you to this event. Please click "Going" so we will know you want to come.
If anyone would like to attend this event, please click the "Going" button.
You are invited to attend this event. Please click the "Going" button.
We want to see you at our next event. Click the "Going" button now.
Don't forget to click the "Going" button is you want to attend this event.
Click the "Going" button to attend this event.
Thank you for your interest in our event. We need everyone to click the "Going" button please.

"If you are coming please certify so by clicking "going""
To certify something is a formal was of describing that you will confirm you are doing something ex. going to an event.
"If you would like to attend the event please click "going""
To 'Attend' something is a formal statement regarding that you are going to be present at a certain event/place.

Both sentences are friendly reminders/requests which tell your guests to click the "going" button on the event page. Using a reminder such as these will ensure that more people make use of the button.