how to correct date already loaded in google

Hello, I created few years ago a calendar

imported it to google calendar

and now we found a mistake in on of the birthdays - the year the person was born is different

I want to correct it 

how can I do it?

I have the ics file from the site - the one that i loaded

now I need,

first - to remove all events of this birthday

second - create new events for this birthday in the correct date.

how can I do it?

this calendar is no appear on the site. any way I can load the calendar from the ics file?

how can I delete all events of this specific birthday?

please assist