@Yiqing1
Several options to fill calendar gaps:
- Lower your price on the dates you want to fill
- Use a Custom Promotion to lower your price (not available until listed for 45-60days)
- Message current guests and offer a 20-30% discount to extend their stay by one day before/after their reservation.
Go to the Help Center on Airbnb to learn more about these topics and/or type a keyword in the Search the Community box at top of the page:

Here is a Guide for New Hosts that also provides alot of tips:
Guide for New Hosts
https://community.withairbnb.com/t5/Community-Guides/A-Guide-For-New-Hosts/td-p/2073093