How to fill return with 2 company cars

How do I fill in my return when I used to company cars within the tax year they were not leased

Do I write the total business lbs for each car or the accumulated business km?

You would do the cars separately so one at a time. Once you have done the first one it will ask you to do the next car.

Do I write the business kms for each vehicle or the complete amount of kms appearing on my logbook

It would be the km which belonged to the different vehicles you used.