Changing Colour Settings to ECI RGB

Once you have the profile downloaded thanks to Per, just be sure that you CONVERT to eciRGB rather than assigning, it's an easy mistake to make. 

Where to place the profile on a mac see this info: https://www.colourmanagement.net/advice/where-are-my-icc-profiles/

IF you can go back to the RAW then I'd render that to eciRGB

I hope this helps
neil barstow, colourmanagement net - adobe forum volunteer - co-author: 'getting colour right'
google me "neil barstow colourmanagement" for lots of free articles on colour management

This profile is not installed by default, you'll have to download it from ECI, here's a direct link:

http://www.eci.org/lib/exe/fetch.php?media=downloads:icc_profiles_from_eci:ecirgbv20.zip

Unzip the file, then install the profile. I'm a Windows user, so I can't tell you how to do this on a Mac.

There is no need to go into Color settings for this.

Create a duplicate of the file (Image > Duplicate), then go to Edit > Convert to profile, choose the eciRGB profile, and save the file. Make that ICC profile is checked in the Save dialog.

You cannot use Export for this, it is designed for creating small files for screen viewing, and sRGB is the only option for color profile.

I'm not sure how relevant this profile is today, but ECI says on this page

"... while there were and still are other reasonable offerings around in terms of RGB working space ICC profiles ECI wanted to see one that … has a gamut that covers all colors that can be printed on today's printing presses - whether sheet fed or web offset, gravure or newsprint - but not much beyond (in order to not to waste precision for bits that never really get used) … produces a neutral gray whenever the values for Red, Green and Blue are equal … offers equidistance, i.e. equal difference between two color values in eciRGB mirrors an perceived equal difference when these colors are seen by the human eye … is based on a Gamma of 1.8 and a light source of 5000K."

If your original file is in sRGB, converting to eciRGB will probably offer little advantage.

If the original is derived from a raw file, it would probably be a good idea to render a new file (using Camera Raw or Ligthroom) in Adobe RGB.