Make a sketch...use graph paper if you need to.
Use the 2 point formula to write the equation of each of the 2 chords, AB and CD
To show that they are perpendicular the slope of the one must be the negative reciprocal of the slope of the other.
Then solve the 2 equations simultaneously. The solution must be the midpoint of CD if AB is the perpendicular bisector.
This solution involves a bunch of algebra...but is NOT difficult.