How do you apply a training schedule?

Well, you have two choises. First, you can apply a training schedule you have created or a custom training schedule to a whole part of the team (first team or reserver for exemple)

In the second case, you will need to apply a schedule to a specific player.

Just hold left mouse key over the selected schdule, and holding the mouse pressed, drag it on the player you want to apply the schedule to.

Don't forget you will need to assign at least 2 coaches per training schedule.