The bow is not sagging. There are 2 straps that pull that bow into position and the straps are probably broken. You will need to take the top off of the frame and replace the straps
You can see the 2 straps in the image below.
I am willing to bet the top is probably super heavy to move too. The bow the straps are attached to has springs in it to help lift and stow the top. so if you raise and lower the top you have zero assistance because the starts are not connected.