It’s usually best to keep all times in UTC (the default on Render instances) and do any timezone conversions in your code, when required.
Changing the timezone on your instance is likely not a good idea, but if you do want to try that, it can be done in the usual Linux way by setting an environment variable for TZ. For example, TZ with a value of Asia/Yangon will make the instance timezone the UTC+6:30 used in Myanmar.