If you're using the PRO version, you may have noticed the lock icons in various places on your schedule:
The lock at the very top lets you lock and unlock all visible games – i.e. taking into consideration any filters you've applied.
The lock next to the Week X heading lets you lock all games under that week (all of these apply only to visible games).
The lock in the grey date heading will lock all visible games under that date.
The lock on each game will lock/unlock that game only.
Locked games cannot be moved, so this is a great way to make sure you don't accidentally change games for which you've already found the perfect spot.
This can be especially useful in combination with the Retry Allocating Games button.
For instance, if you have unscheduled games after the initial schedule generation, you can lock the games that have been scheduled (or some subset of them that you want to lock in place), change/remove/loosen some of your constraints and rerun the allocation only on the unlocked games.
By iterating on this process, it is often possible to arrive at a finished schedule without having to do much if any manual work.
Locked Games on the Calendar
On the calendar page, you will see locked games denoted with a dark outline.
You can enter lock/unlock mode by clicking the corresponding button at the bottom:
Once in lock/unlock mode you can click any game to toggle it's state from locked to unlocked and vice-versa.
Turn off lock mode by clicking the button again.