On time for the start of the new season we have made major improvements to the management and handling of training periods / sessions. When you go to the menu item Training Ground and select Sessions you will now see all training periods on top of the sessions. You can select the period by clicking on it and will now only see all the sessions that are part of the period. By clicking on it a second time you close the period and go back to seeing all sessions of the selected season.
If you have not created a training period so far or want to add a new one, just click on New Session and select New Period.