If your Airpods are not able to connect to the Apple watch then the reason behind it may be an outdated version of watchOS.
Let us tell you that Airpods will only be compatible with watchOS 3 and newer versions.
So if you want to update your Apple watch then you will have to follow the below mentioned steps:
Step 1: Open watch app
Step 2: Select General option
Step 3: Tap Software Update