Would a little milk work mixed with tuna, sweetcorn and pasta bows? Or does it need a little flour to thicken?

Answer 1

make a bechamel sauce with the milk & flour (season well with pepper and/or nutmeg)
then add the tuna and the corn
mix in the pasta bows and garnish with freshly chopped parsley or dill

voila!

Answer 2

Yes, you would need flour to thicken.
This would make a tuna a la king type of meal.
A little pepper and maybe your choice of other spices would help the flavor. Sounds good to me.