phpmyadmin is a database management tool that is usually supplied by your hosting company.
some hosting companies use other tools so you will have to check yours.
most often the hosting company will be using CPanel for managing your website, if so, then phpmyadmin will be
listed in the database section.
open it up.
on the left side, you will see a list of databases that are installed on your computer.
you want the one that your phpbb board is using. If you do not know the name of it, check your config.php file in
the ftp. It will be in there.
once you know which database is the one you want, click on it one time in the left menu.
click on your database
when your phpbb tables are in the right hand window, click on the export tab at the top.
click on custom
on the next page:
select all tables
check: save output to a file
tick: structure and data
check: add drop table
check: include column names in every INSERT statement
uncheck: Dump binary columns in hexadecimal notation (for example, "abc" becomes 0x616263)
click Go
it will ask you where you want to save it to.
pick a spot on your computer that you can find later.