There is NO simple process.... You will need to pick an easa country and look at there icao conversion process...
Most straight forward is Ireland , followed by UK........Last Germany
In effect its 14 ATPL exams ( or 13 CPL exams ) depends how many hours you have will determine what minimum flight hours you need to complete ....
The CPL modular is 30 hours flying.....the more hours you have, will reduce this number
A Class 1 medical, An english language proficiency test and a flight radio operators licence is also required.
For IFR Same thing a IFR skills test in a multiengine helicopter , if you have an FAA IR reduced hours are available but must have a multi engine type rating