Click the Protected Item that you want to change the schedule on

From here, you can click the green "+" button to create a new schedule or select an existing schedule

To edit an existing schedule, click the blue pencil (edit) button.

In the General tab, you can change the schedule's name, where the schedule stores the backups, and specific settings for when the backup runs. Clicking the Time tab will let you change the schedule itself.

You can click on the dropdown to change the frequency of the backup.

There are various options that can be further customized.

How to edit a schedule