If you mean you don't know how to copy a map from a different version to an other map, then set both maps to the same client version, for example the 8.6 map to 8.4 (Map, Properties, Client Version) and save.
Then open the 8.4 map, click File, Open, and open the second map you set you 8.4 and it will open in the same Remere window, if you click copy then you are able to paste it in the 8.4 map.