Applying bitmap is quite easy, follow the steps below.
Step 1: Navigate to Rendering -> Material Editor..
Step 2: On new windows open -> Material -> Get Material
Step 3: New Windows will again open, double click on VRayMtl
Step 4: VRayMtl will be selected -> Rename it -> and click on select box in front of “Diffuse selector”
Step 5: New Window will open -> Click on Bitmap
Step 6: Navigate to image folder -> select the image -> Click Open
Step 7: Drag and drop the Material selected from Material Editor to the viewport Object -> change tiling according to your bitmap and object size
Step 8: If the bitmap is applied properly then you not need to follow this step, if not okay them apply the modifier.
Navigate to modify tab-> click on the dropdown of modifier list -> select UVW map -> change it to Box or play around according to your need.
Feel free to ask questions in the comment section.