I want to help you, but the euro conversion tool for NAV is out of Office deployment support scope.
Here is an article "Setting Up Dynamics NAV" which is related to the functions of Dynamics 365, if you have any further issues on those functions, I suggest you post a new thread on Dynamics 365 Community.
Thanks for your understandings.
Besides, if you need to use the tool in Excel app, please check whether the Euro Currency Tools Add-in and EuroConvert Function are helpful (There is no Croatia ISO code yet, we need to see if there is the new ISO code updated in next year.).
Hope the information is helpful to you.
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