Welcome to the Ranch
Please think carefully about what you are planning to do. You look as if you are adding six numbers. Is there any difference between the types of the numbers? Then you seem to want to print them out in pairs. Are you adding numbers or pairs of numbers? Remember two numbers do not constitute a pair. Are you adding six things or three?
Start by going through that loop, without the List, and get it to print
1,2
3,4
5,6
I tried to change the loop index but that also didn't work.
That looks as if you are guessing. Don't guess. Or do guess. You can take a million guesses and as long as they are different, there is a good chance you will get a correct solution. Somewhere…
Or you can think about it and work out what you want to do and get it to work first time.