You can't. Knowing the volume doesn't tell you the dimensions. There are an infinite number of different rectangular prisms, all with different dimensions, that all have the same volume.
Here's an example. Let's say I have a rectangular prism and its volume is 64.
The dimensions could be . . .
1 x 1 x 64 1 x 2 x 32 1 x 4 x 16 1 x 8 x 8 2 x 2 x 16 2 x 4 x 8 4 x 4 x 4 .
If I only tell you the volume, there is no way to figure out the dimensions.
