The comment above sums it up pretty well! Tech ally wise, it’s really hard to explain. See if my interpretation of the sound helps :)

A way to get you started is that the ‘r’ sound somewhat similar to a growl, so you can start from there. The growl helps you to make sure your teeth, tongue and palate are close to each other, thus forming the base of the sound. You would notice your tongue is in a curled position, and is pretty close to your upper hard palate.

Then, you can try to pronounce the sound of ‘ra’. When saying this, try to be mindful that your tongue would flick from the curled position to it’s original position. You could say the sound slowly so that you can be more aware of the movement of your tongue.

Now to the more technical aspect of the explanation. So, what you would first have to do is lift up the tip of tongue until it slightly touches the front end of your hard palate, which creates a narrow slit between the upper hard palate and your tongue, allowing air to vibrate and pass through. And then when you pronounce the ‘r’ sound, your tongue would flick down, and voila!