Hello, sorry for the late reply.
You have two options here, one easy and one slightly harder, and they both include the use of a VRTK interactable (there is a tutorial about it on the academy) and Unity hinge joints (plenty of tutorials about these on YouTube).
I don't know how much you are familiar with these two, but briefly:
Interactable: VRTK prefab with all the scripts and components you need to have a grabbable and interactable object. In its hierarchy, there is a child called Mesh and it contains the visual mesh you need to change with your custom mesh (in your case, that would be the door or the handle).
Hinge joint: type of Unity joint perfect for doors, you can set degree limits and also spring and damper if you want the door to close itself if released.
Going back to how to create the door, your options are:
1 - the easy) drag and drop a new interactable second follow, which will come with a rigid body attached - disable use of gravity. Substitute the default mesh with your door. Add a hinge joint component to the top level of the interactable. Add the collider of the door to the top level, where the hinge joint is. If you want to attach the door to a wall, the wall needs a rigid body too. If you can, freeze all wall's position and rotation, disable gravity and make it kinematic (if you can't make it kinematic, I'll suggest you create a new object with a rigid body on it, so you won't affect the wall).
Set up your wall as attachment of the hinge joint in the interactable.
Now you need to do some tweaks on the hinge joint, and I'll suggest you follow a generic Unity tutorial on how to make doors with hinge joint. You have to set up the anchor correctly, otherwise it won't work.
Once you've done this, there's one more step to do in the interactable. Going inside its hierarchy, you have to find a child called something like Interactable grab primary action, which is quite nested into sub children. Once you found it, you have to change the grab mode from follow transform to follow rigid body.
You should have a (hopefully) working door.
However, the door will be grabbable from any point, not only from the handle. To have only the handle working, it requires some extra steps, depending on how accurate you want it to be.
You can either remove the door collider, and have it only on the handle. This way you can only grab the handle, but you won't have collisions on the door itself.
Or, you can go to the slightly harder option.
2 - harder) this requires the use of two joints: hinge one for the door, and a fixed joint for the handle.
Therefore, take your door and separate the handle from the door. The door won't be an interactable this time, so create a simple game object and create a hinge joint for the body of the door and attach it to the wall, as already described before. The handle will be your interactable, so drag and drop a new interactable prefab and use the handle as its mesh in hierarchy. With the handle collider still on the top level, you have to create a fixed joint on the interactable and attach it to the body of the door, which will require its own rigid body. Fixed joints are very simple to use, but if you are struggling with setting it up, again, there are many tutorials for it online. The fixed joint will make sure that if you move the handle, the door will follow the movement and they will act as glued together.
Remember to always change the grabbing type to follow rigid body.
That should be it.
Building it further, you could probably substitute the fixed joint of your handle with a hinge one, with a spring and damper to have a twistable knob or handle and, in code, detect joint's degrees to unlock the door and open it
Let me know if you need clarifications on any point! 😃
Have fun with joints!!