Are you referring to the Wordpres "User" account? I'm not sure I understand the issue. Did you create another user with administrator privileges? In that case the user ID is probably 2, if you have no other users. You can check the ID with the following commands:
mysql -u root -p bitnami_wordpress -e "SELECT * FROM wp_users;"
So if the ID is 2 then you can change the password in the following way:
mysql -u root -p bitnami_wordpress -e "UPDATE wp_users SET user_pass=MD5('NEWPASSWORD') WHERE ID='2';"
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