A coroutine runs at the same time as everything else. It does not “pause” execution. So your coroutine at this point does nothing but count up 6 seconds in the background while the game is running.
Try moving the code that changes force inside the coroutine. In other words your coroutine should:
Set the force
Wait 6 seconds.
Reset the force.
Right now you are essentially doing:
Set the force.
Start counting 6 seconds but also Immediately Reset the force.
You could edit your post to use code tags, then it would be so much easier on the eyes…
You could also make your Coroutine more flexible by passing the item that is to be run as a parameter.
This way you could use the same code for different things you need to delay.
i.e.