Hi I have seen many posts with similar questions, but not one that I think completely fits my problem.

I am working with the European Values Survey and I would like to add a variable with data from an external source, that describes the percentage of the population that is immigrant of each country that is included.
My dataset consists of panel data of many individuals in European countries, so the observations of this percentage should be linked to each individuals and should match with the country they live in. I do not know how to add these data, let alone connect these together. I really hope someone can help me with this. Thank you so much in advance.