This goes in Help & Requests. Ignore the Legacies of Dondoran part - that is just a joke.
Anywho, the Move Toward Target setting is done in the Weapon Animation section. Go to the Item Tab, and for whatever weapon, click the Weapon Animation button. In the new screen, set every character to Move To Target in the droplist near the top.
Now, if they have that weapon equipped, they will move to the monster and attack.