To sync HiChee's calendar with your existing calendars, you will first need to export those calendars as a link.
Here is an example how to export your calendar from Airbnb.
Go to your listings page, select the listing whose calendar you want to export, and click "Availability" as shown in the picture below.
Under the "Sync calendars" headline, you will see the "Export Calendar" option; when you click on that, you will receive a link to the exported calendar. Copy that link as you will use it for importing.
And here is how you export the calendar from VRBO.
Go to your account and select the listing whose calendar you want to export.
Click the Calendar icon in the left navigation menu, and click on the Reservations as shown in the picture below.
Click the Import/Export arrows icon, and click the Export Calendar. You will receive a link to the exported calendar. Copy that link as you will use it for importing.
Once you have the link to your calendar, navigate to Calendar & Pricing under the Host tab.
Scroll to the bottom until you find Sync Calendar and paste the link you have just exported in the Import Calendar field
For detailed information, please read this article.
If you have any further questions, we are more than happy to help!