Click your user icon (1) in the top-right hand corner of the screen and click ‘Settings’ (2):
On the left-hand side of the screen, locate the ‘Intervals’ (1) option and click it:
If you want to edit an existing Interval, simply click the field and begin typing the new label. Otherwise, click the ‘Add New’ (1) button:
Enter the ‘Interval Label’ (1) and click ‘Save’ (2):
Your newly created Interval will be in the table:
