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