Not really a guide, as when I did it, I just had ChatGPT help me out and YOLO'd it. But what I'll tell you is that you need to select all (of the objects in Daz), then when you've done that, you export it as an OBJ or a FBX (I recommend FBX) into a folder of your choosing. Then, open Unity (2018.1.9f2, VaM only works with this one, you can download it for free), import the textures from the runtime folder of Daz3D you had into the Unity Asset Tab, then import your OBJ/FBX file which holds the exported environment. It should automatically assign the materials needed onto the FBX/OBJ mesh. If it looks finicky, you can make your own materials and put in the Color, Normal, Roughness and Metallic maps into it yourself and then drag the material onto the surface in the FBX/OBJ that you want it to be on. Ex: Dragging custom wooden PBR material to the bottom of the object.
Make sure you check generate colliders (on the Inspector tab) so it automatically makes the environment interactable by VaM characters when you import it later. Also, make sure the object in the Unity scene is at the world origin, specifically under the default directional light. For most cases, you can do this by setting it's X, Y and Z positions to 0 in the Transform tool on the right of the screen. If it doesn't look like it's 100% in the middle, you can adjust it yourself to your liking.
Once you've done all that, drag the model from your Hierarchy folder (on the left) back into the Asset Folder on the bottom. This should save it as a .prefab. On the bottom right, you can see it with its AssetBundle named "None". Click that, and press "New..", this will create a new assetbundle for you to assign the prefab to. Once you've named it, it will assign that assetbundle to it. Now, go back to your assets folder and create a new folder called AssetBundles. Then, create a new folder called Editor and inside of that folder create a C# script called BuildAssetBundles with the following code inside it: (attached .txt file)
After that, on the top of your screen, go to Assets > Build AssetBundles. Make sure that you actually have a .prefab under an asset bundle as I mentioned before, otherwise, this will do nothing. When it's done building it (it takes some time), you will see the assetbundle and its meta file in the AssetBundles folder in the Assets folder. Go to its file location by right-clicking > Show in Explorer, this will open up the AssetBundles folder in your Windows Explorer. I recommend that you pin this to quick access along with the Unity file folder whenever you wanna repeat this process. Now, in the AssetBundles Folder in the Explorer, copy ONLY the ones listed as File types, not the MANIFEST or META ones. Go to your VaM folder, then to Custom/Assets and then paste it in there. Then, make it an accessible assetbundle by adding .assetbundle to the end of it, and you're done!
Open VaM and add a CustomUnityAsset from the add Atom panel, it's under Misc. When you've done that, go to the asset and load in the file, it'll pull up the VaM File Explorer. Go to the path that you saved your .assetbundle in inside Custom/Assets and click it. After that, just load the CUAasset like usual, and now it's in your scene. Hooray!
It's honestly not that hard, I just wanted to describe every little thing so you wouldn't get messed up. I'm assuming that you already know half of this stuff, have fun!