To adjust a schedule that is already running you will go into the campaign. This will open up the steps. On the upper left corner you will see an icon that says 'Schedule Default' under the Inbox and Steps tab options.

Once you select that, the schedule info will pop up. To add a new one go to the drop down arrow next to the time zone and select 'Create new schedule'.

You can customize the new schedule, name it, and select it as your new schedule. To learn more about how to set up a sequence and create a schedule you can refer to this article.