The conventional current is the movement of charges from the positive terminal of the battery to the negative terminal of the battery. On the other hand, electron flow is the other way round - i.e. it is the movement of electrons from negative to positive terminal.
Now, one may immediately notice the one core difference between these two statements: conventional current assumes positive charges are moving, while electron flow assumes that electrons are moving. In reality, it is the electron that is freely moving to conduct a current, as we know that the “positive charges” are simply the ions in the metallic lattice held fixed in place. So why then is there a need to have a conventional current?
The answer to that is pretty simple: it just so happened that people discovered the freely flowing electrons a little later than the concept of current. In other words, people used to believe in the conventional current before the electron became the new norm. Fortunately, this shift wasn’t that catastrophic, as it only differed from the original in terms of direction!