To set up Razorpay Webhook first head over to Payment methods > Razorpay
Now enter your Razorpay Api credentials and save.
Once you save, you will get a webhook url
Now Copy the webhook url and head over to Razorpay to enter your webhook url.
Please follow Razorpay instructions to know where to enter your webhook url https://razorpay.com/docs/webhooks/setup-edit-payments/