Re-downloading Lightroom 6 on to my new MacBook?

Back in 2015 I purchased lightroom 6 on amazon for PC, three months later I purchased a Mac Desktop and (I don't remember how?) downloaded Lightroom 6 onto there, where its been since I downloaded it. 

That computer has since become outdated and I've recently purchased a Macbook Pro and want to re-download Lightroom 6, but can't find a download link? 

My Amazon link is for PC and I don't remember how I re-downloaded it in the first place.

Any help would be appreciated. Thanks!