Monotonicity error in Lookup table

Hello, I am using an excel file containing 3 sets of data, I want to show the dependency of the first coloumn to the two other coloumns, therfore I am using a 2D Lookup table (2 inputs and one output) I got an error that the indexes ( table inputs) should be monotically increasing, but it is not possible to sort my two inputs of the lookup table incrementally at the same time! What shall I do to implement these data in a lookup table?!