when you make a square bezier it’s not an editable spline until you hit the “C” key or convert to editable object. After you have done this go into point selection mode and use the “add point tool” switch views to front, and add your point. If it’s not right in the middle, make sure that point is active and move it to the middle using the viewport grid. once in the middle, move point up to your liking. The convert that point to soft interpolation and drag out handles to get your desired curve.
I’m only half the thing I say I am, the other half are me.