So my flight is booked & paid from London to Bangkok but I just can't seem how to enter the Advance passenger information that's needed.

I booked flight online.I've gone on to manage my booking & logged in &  it gives details of flight & seat booked etc

At the very end it says NOTE and shows 4 lines

+ seat selection

+ meal order

+ online check in

+ advance passenger information

when you click on the + it says...Please enter Advance Passenger Information(APIS) as required by US immigration authorities. This information will help streamline the check-in process.

 

But I cannot see how to enter my information...can anyone help ? the offices are closed at the weekend

As you're not flying to the US, presumably APIS is not needed by US Immigration Authorities, and Eva aren't interested in collecting it – it's totally irrelevant for a London-Bangkok flight. Forget about it, is my advice, at least until Monday when you can talk to the airline.

Maybe from the basic account profile page?  I used EVA a lot but have not gone in to the site in over a year.