The LINE containing the diameter would contain the circle's center of (2,-3), AND also the origin (0,0). You could put limitations on the domain for the line to achieve just the diameter segment; but in any case, you can find the line containing those two points. The equation for the line is .
Find the endpoints of the diameter using the equation of the circle and the equation y=-(3/2)x. Substitute for y in the circle equation, solve for x, and find the corresponding y value.... you have the endpoints of the diameter.