so please help me how to import old data into new mysql
If the ispconfig version on the old server was not the latest release, then follow these steps:
1) Make a backup of the ispconfig database.
2) Replace the ispconfig database with the ispconfig database from your backup.
3) Edit the file /usr/local/ispconfig/server/lib/config.inc.php and set the ispconfig version number in that file to the version number of the old ispconfig system.
4) Run the ispconfig update so that ispconfig updates the database structures.
Regarding the website databases, just restore them from your backup. One thing that you have to do afterwards is that you copy the mysql users and databaserecords that are in the mysql.user and mysql.db database tables to the same tables in the new mysql installation.