First you should create a new database on 000webhost.
CPanel -> MySQL
Take note of all the data you use to create the database (server name, name of the database, the DB user and password from the DB).
Then you must from your PC Import your database to 000webhost. This can be done using cPanel -> phpMyAdmin -> Import (button on top).
Finally you must change your forum settings to use the new database.
Do not forget to save BD and files backups in your PC.