Spring goes on the thick black post, then the pinch roller assembly.
The arms of the spring should lock in such a way that the pinch roller is kept away from the capstan. The pic is that of JVC M80 deck. So hard to show how that spring is locked in place without actually working with it.
One end will be locked on the chassis with tension and the other on the pinch roller assembly to keep it away from the capstan when play is not engaged. When play is engaged whole assembly moves and gives pressure to the pinch roller and capstan for tape transport.
You can see that 90 degree bend is resting on the top of the inch roller assembly. So the other one has to be somewhere on the chassis to give tension to the spring.
See that lip like projection on the side of the screw. Not near the screw but next to the screw. That is where the straight end of the spring rest. Then you need to turn the spring and then slip the 90 bend side over the pinch roller assembly. That is it...