amazon rds doesn’t allow you to change timezone, it keeps same utc time zone across all regions. time_zonevariable in the parameter group is read only.
you can change the time zone on each connection or session by making a procedure in default mysql database and call this function on each init connection.
1.    create a procedure for ist
delimiter | createprocedure mysql.rds_store_time_zone ()ifnot(position('rdsadmin@'incurrent_user())=1)then set session time_zone ='+5:30';endif|delimiter ;
2.   update parameter group
aws rds modify-db-parameter-group --db-parameter-group-name parameter_group_name --parameters parametername=init_connect, parametervalue=call mysql.rds_store_time_zone, applymethod=immediate
3.   grant execute permission
grant execute on procedure mysql.rds_store_time_zone to 'user'@'%';