How can I pair with one airpod and I lost the other one

I'm not sure but I think you can if you use them on an android, or as an android.

You manually reset them with the button on the back of the case, then open them and hope the Bluetooth turns on, and you'd either get the pop-up card on your phone, or you can try to connect them manually on Bluetooth, I think the documents that come with them explain how to do it buuuut, you'd be better off getting a replacement, and they're cheap on eBay so you can get one there and repair it the same way.

Hi, mubarak190, and thanks for reaching out. We see you'd like some help pairing your AirPod. We'll be happy to assist.

You'll need to follow the steps here: Connect your AirPods and AirPods Pro to your iPhone

However, do keep in mind that AirPods are meant to be used as a set. If you are unsuccessful in pairing them with only one AirPod, you may need to reach out to Apple to inquire about purchasing the missing one: AirPods Replacement, Service, and Repair

We hope that helps.

Cheers!