Populating logtime for @timestamp

If so how do I convert it back? I can see something like 'Z', 'ZZ' and 'ZZZ', found that they are for timezone. I want to add +0530 since our timezone is related to Asia/Kolkata. How can this be achieved?

I checked the log, but there is no data in that. It only pertains logs till start of logstash agent, apart from that there is no data regarding indexing.