janalice,
There's a thread dedicated to
Eurocypria here. There contact details are on there
website. As they are a Cypriot airline, you'll have to call Cyprus to speak to them. If the flight is chartered by Thomson Holidays, then seating will be handled by Thomson (unlikely in this case). You can select your seats with ECA online,
click here. I wouldn't worry too much about pre-booking seating. As long as you're at the airport in plenty of time, you'll get seats together, especially if you're travelling as a couple.
Darren