Then, open up the "aircraft.cfg" files of the respective aircraft and input the following text after the last aircraft entry, before [General] and after the description of the last entry. Change [fltsim.xx] to the next corresponding number (for example if the last entry was [fltsim.2] you would input [fltsim.3] replacing the xx with the number 3).
(If it does not open initially, right click the *.cfg file and select "Open with..." and select "Notepad")
A340-200:
[fltsim.xx]
title=A340-200 SriLankan Airlines
sim=TomA342
model=
panel=340
sound=
texture=SLA
kb_checklists=
kb_reference=
atc_id=UR-ADD
atc_airline=SriLankan
atc_flight_number=7820
atc_heavy=1
ui_manufacturer=Airbus
ui_type="A340-200"
ui_variation="SriLankan Airlines"
ui_typerole="Commercial Airliner"
ui_createdby="Thomas Ruth"
description=Sri Lankan air lines livery for Thomas ruths Airbus A340-200 by Dulshan Wijayasinghe.