I'm a BJJ coach and run bjjtech.com and covered this question over there. Here it is:
Setup: The Initial Situation
You are standing inside his de la riva guard. He is setting up any variation of the De la Riva guard where his leg is wrapped around your lead leg. This might include him also gripping your sleeve and applying pressure to your rear leg with his other foot. Much of this technique applies to gi only, but can be adapted for no-gi. In this example, his left leg is wrapped around your right lead leg.
Steps
Grab the end of his left pant leg with your left hand. You will be reaching slightly under your right thigh to reach this.
Quickly turn your hips, pivoting on your right foot, spinning your left leg behind you. While you are turning your back to him, you will maintain control of his right leg and land tight around his left thigh.
Immediately and strongly clamp your left thigh on his left leg above his knee. Your right foot should be planted inside his left thigh and should be touching your left thigh. This will ensure you are as tight as possible.
Grab his belt or the top of his pants with your right hand. This will maintain control of him as you kneebar him and will help prevent him from improving position momentarily.
Lie to your left and extend the kneebar
More detail
Here's a link to the full technique on bjjtech.com.
And a link to the embedded YouTube video.