You can use google flights. See the support pages.

You can search up to 5 destinations at a time
Restrict to Sky Team
Set firm outbound date
Change return date and use + or – 2 days, repeat with new return date.

Example: Outbound is day 1. Earliest return is day 6.

First search is return day 8, +- 2 days
Next is return day 13, then day 18, etc. until you’ve either planned to move there or found what you want.

More ITA coding info here