Garmin Zumo 595 firmware on a Zumo 590?

New to the forum. Stumbled across because there was apparently a post on this forum about using Zumo 595 firmware on a Zumo 590 (hardware wise, they seem to be near identical units).

I was told the post was lost in a server crash here and was not on the backups when it was restored.

Does anyone have any info/instructions on this?

Thanks in advance!