User you're using blameshift_smf718 should have all privileges to both SMF and phpbb databases. So you should seek for "add user to database" or something like that in your cPanel - mysql databases.
Something like this:
https://www.liquidweb.com/kb/how-to-assign-a-user-to-a-mysql-database-in-cpanel/
Тhen manage that user to have all privileges to both databases, and you should be good to go.
I've tried that after re-installing again recently, it and nope still stuck with this
Sorry, the database connection information used in the specified installation of SMF cannot access the installation of phpBB3. This may either mean that the installation doesn't exist, or that the Database account used does not have permissions to access it.
The error that was received from the Database was: 1142
this is really annoying,.might have to cut my losses and just start from scratch cause this isn't working