Concatenating three columns into one

Hi,

Hope you guys are doing great.

I have a requirement that I am trying to resolve and have been struggling to make it work so far. We have a multi-select picklist on opportunity object called Reason Won/Lost, this picklist has multiple value, and users goes in and select them. One of the requirement is to show their corresponding codes instead of values on report (I was able to do that by Bin function on reporting side), but the problem is that all the values show up in a separate column and now i have to combine them into one single column, i tried concatenate function but