What can i do?
You already have a license or a specific part of a license, but you want something different. This can be anything. Do you want an add-on like flying another type of aircraft, you can find information under class ratings (A) or type ratings (H).
But if you got your license in a so-called 'third country', and want to fly in Europe, you will normally need to convert your license into an EASA license.
E.g. if you did your flight training in America, you can only fly N-registered aircraft over here. What you need to do to convert your license depends on your experience.
When you obtained an Instrument Rating on a Single Engine, and now need it on a Multi Engine, you can also do a conversion.
Having a license for fixed wing aircraft doesn't mean you can fly helicopters, or the other way around. But it does mean that you can use parts of your license to do a conversion. So if you want to fly both, you don't need to do the complete training from scratch.
Adding Performance Based Navigation to your Instrument Rating is also considered a conversion because you won't need to do the whole IR-training again, you just do some hours to convert it into the new style IR with PBN.
There are plenty possibilities and even more rules about what you can or should do.
We know most of them, but if we don't know, we will figure it out for you.