I tried using this but this did not make any difference. but when i tried to convert this string "theyââ¬â¢re" to normal text with $ZCONVERT i am getting below result.

Example:

set rawString="theyââ¬â¢re"

USER>Set fixedString = $ZCONVERT(rawString, "I", "UTF8")                         
USER>write fixedString
theyâ?re

So, my Question is how to remove the â? and get the exact text. and this is not the only text that is coming we can also another character encoding as well.

Yes, that's correct. It's coming from the REST API in json payload.

Got it @Enrico Parisi 
So is it a correct way to use ..%RequestHeader.TimeCreated in BO...I mean will it give the exact time?