What is the procedure to change Timezone ?

[Vincent _BleuLemon_]

Hi Guys,

A customer experience some timezone issue with REST APIs used in some integration with Qlik.

Their JIRA Server has been installed few years ago with a wrong Timezone (Los Angeles instead of Paris). It had no effect until now, but today, since they want to extract data to Qlik, they expect to have the correct date.
The REST APIs does not take in account the Timezone of the account nor the JIRA Timezone, but the System Timezone.

What should be the correct procedure to change it (System TZ) ?
Is there some change to do in the Database Timezone and/or JIRA Timezone ?

Thanks by advance
Vincent