How login on mysql

Hello, I just install mattermost with docker one line.

¿How can enter on mysql database for get all the conversations? My boss want export all every week.

Something like
docker exec -ti mattermost-dev /bin/bash
$> mysql

Please help me.
I want to enter Mysql.

to access your MySQL type:

mysql -u USERNAME -p

you are typing:

$> mysql

and you do not need to type “&>

To export a database in MySQL you need to do this:

Assuming your MySQL username is USERNAME and your database name is DATABASE.

Then export your database by typing this:

mysqldump -u USERNAME -p DATABASE > DATABASE.sql

How Could I know Username and password and database name?