Convert Incoming UTC timestamp to local time

Elastic Stack Logstash
1

Newbie here, Is there a way to convert the incoming timestamp from my log file into my local timezone,
e.g. my file contains the timestamp in UTC "2017-12-01T07:30:32.425064Z", is there a way to convert this into "2017-12-01T12:30:32.425064", which is for my local time (Asia/Kolkata).
I tried the below:

date {
match => ["datetime", "ISO8601"]
timezone => "Asia/Kolkata"
target => "datelog"
}

However I am getting the same value for datelog field as for datetime. The reason for doing this conversion is some of my logfiles have a timestamp of UTC and some have local timestamp (Asia/Kolkata).

Any help or pointers appreciated, or am I wrong in my assumption that this conversion can be done in logstash?
Thanks!

PS : Not sure why some of the text above is coming in bold.

2

Ok so I went the other way round, instead of converting to my localtime zone, I converted the logs in localtime zone to UTC, Kibana takes care of converting them to my localtime.
Consider this closed.