Lightly scrunch the mixture together with your fingers and add more corn until you’re happy with the tuna:corn ratio. It’s a subjective thing so don’t ask me for stupid quantities; hey, we’re not talking Delia Smith here. Then, add some mayonnaise and gently mix until it all appears to stick together in a mayonnaisey goo. Again - use your judgement, but just don’t overdo the mayo ‘cos you don’t need very much. If you and/or your guests are people of refinement, taste and culture, it might be cool to add some salt & pepper at this stage.