AddIns are not backwardly compatible so you cannot run a 10.3 AddIn on a 10.2 or earlier install. The only way to get that addIn running on a 10.2 is to recompile the Addin on a 10.2 machine, but be aware the AddIn may be using objects/code that exist in 10.3 but not in 10.2 so may need to develop a work around.