Again, a "plain conversion" isn't always possible.
It depends on what kind of profile you are starting with, and what kind of LUT you are trying to create.
And even when it is possible, you need more information -- ICC profiles are standardized, and tied to color appearance standards. 3DLUTs are not standardized, and contain pretty much random mappings (so you'll get different results for different encodings and colorspaces).
ICC profiles generally are tied to CIE L*a*b* or CIE XYZ, while 3DLUTs can be designed for linear, log, Rec709 encodings and many different primaries and whitepoints.
It's like you're trying to use a current smartphone (ICC profiles) on a network from 1990 (LUTs) - in some cases it might work, but only in limited circumstances, and you certainly can't use the full capabilities of the modern tech. To make it work at all you'd need details on the exact interchange needed.
Another way of explaining it: 3DLUTs are more comparable to adjustment layers (or groups of adjustment layers) than ICC profiles. Only two types of ICC profiles (device link and abstract) are even comparable to 3DLUTs (and still not quite directly). Display profiles, print profiles, and colorspace profiles really don't match the 3DLUT concept.