How to replace all items meeting a given criteria in a list

I've been using this post (how to do replacing-item in use nested list) as a guide to work out how to replace items in a list, that meet a given criteria.

Specifically, I want to replace all zeros in a list with the value = 0.5. However, the code I've come up with only seems to replace the first zero in the list and I can't seem to work out why.

This is my code:

to-report A-new-list-without-zeros [old new the-list]
 let A-index-list n-values length the-list [?]
 ( foreach A-index-list the-list
   [ if ?2 = old  
      [ report replace-item ?1 the-list new ]
   ])
 report the-list
end

And this is what happens:

observer> show A-new-list-without-zeros 0 0.5 [0 1 0 5 5 0]
observer: [0.5 1 0 5 5 0]

Any help would be much appreciated! Thanks