Hi.. How to convert datetime from GMT to user's local timestamp? i.e 25/06/2

Hi Sharmilan,
Try the text function passing with the user's local time stamp as rule input as shown below :
text(ri!datetime,"dd/mm/yyyy hh:mm")
Hope it helps.

You may find local expression function of benefit.

For the text() function, the datetime should automatically display the user's local timezone (or the Primary Timezone in the Internationalization Settings, if the user's timezone is not set). If needed, you can also use the local() function to offset the datetime (https://goo.gl/e0pn9c).

There are probably a number of ways to do this, but I was able to get something similar to what you are looking for by doing:
datevalue(pv!dateTime)&" "&time(pv!dateTime)