The following instructions are from HomeAway and can be found on their help forum here.
1. On HomeAway
Sign into your HomeAway account
Click Export Calendar
Copy the URL
2. On Uplisting
Select the listing on Uplisting you wish to sync with the HomeAway listing above
Select the 'Connect' button on the HomeAway row
Paste the iCalendar link copied from HomeAway (above), shown in figure 1 below.
Click 'Next sync availabilities' button to export your unavailabilities to HomeAway (instructions below).
Figure 1. Import bookings from HomeAway using iCalendar