I recently purchased a standalone copy of lightroom 6 and am having difficulty in making the NIK collection work with it, I have removed all previous versions of it and done a fresh install twice, the install says it is going to add to lightroom six and it doesn't seem to.
It has happily installed in into elements 2018 though.
... and am having difficulty in making the NIK collection work with it ...
What difficulty? Explain in detail. If there are error messges, please quote the exact complete unedited word-for-word error messages.
No error message but I can't edit using NIK collection in lightroom, it doesn't seem to be an option, could it be I don't have the correct preferences set