Postgres DB Timezone Change
You can change the parameter by editing postgresql.conf or with ALTER SYSTEM via SQL. Don't forget to reload the database.
But you should tell the application development team that they have messed up. If the application relies on a certain setting of timezone, then the application has to set that parameter itself. The parameter can be changed using the SET SQL statement.
If you don't care about time zone handling by PostgreSQL at all, you should use the data type timestamp without time zone.