It's easy to check-in for future days in ZERO. Here's how to do it:
1. Go to the check-in page. You can get there by clicking on the check-in email or by logging into ZERO and going to the Dashboard and then selecting "click here" in the check-in alert at the top.
2. On the check-in page, select "Change" next to the date at the top (click on the light blue text).
3. In the popup, select the day (or days) you would like to check-in for by clicking the dates on the calendar. Then click Save.
4. For "where are you working today?" > select one option (Office, Remote, or Other) and follow the steps to complete the rest of the check-in.
5. Then click on "Check In" at the bottom of the page.
You have now completed a future desk check-in!
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Other helpful tips:
You can always VIEW and CANCEL your future check-ins by going to the "My Check-Ins" page. Simply go to the Dashboard > select the "..." in the upper right hand corner of the dheck-in alert > then select "My Check-Ins" from the drop down list. 
On the "Active Check-Ins" tab, you can see you current and future check-ins. You can delete future check-ins by clicking on the red trash can in the table. You can also see your past check-ins and any check-ins you've created for colleagues from this page as well.