That partially depends on how you're playing. The PC Client includes a big 'X' in the upper left corner of the screen (over where your Digimon's portrait is) that will let you exit and save. Mobile doesn't have that. However, the other way to force a "manual" save, without being on PC and using the 'X'it, would be to go into settings, exit settings with autosave on (this saves the game), re-enter settings and turn autosave off, rinse and repeat whenever you wanted to save. Why do you want the manual save? Genuine question, not meant as an attack.