You need to have installed a MySQL server for Mango to connect to, and created a database with a properly privileged user, before you can convert your existing H2 database.
Once you have that, you will use this section of the env.properties to connect to MySQL (you need to remove the # before the property or it is a comment!):
# MySQL database settings. Your MySQL instance must already be running and configured before this can be used.
#db.url=jdbc:mysql://localhost:3306/<your mysql schema name>
#db.username=<your mysql username>
#db.password=<your mysql password>
#db.mysqldump=<location/command for mysqldump executable for backups>
#db.mysql=<location/command for mysql executable for restore>
"mysql schema name" == "database name" there, with this MySQL server installed on the same machine Mango is on.
and then in the convert properties you have shown you need to use your H2 settings to identify the database to convert. It's a good idea to comment these lines back out after the conversion, but it will not convert it twice by itself. Probably,