There are two springs on the bobbin case of a rotary hook machine like the 180 and I suspect you're talking about the thread tension spring on the outside of the case - this is held on and the tension adjusted by a two very small screws. The other spring is the brake spring which is a complicated shape spring that sits in the bottom of the case and puts a slight amount of pressure on the bobbin itself. Assuming the thread tension spring has been recovered along with its two screws, it should be fairly self-evident how it fits back onto the bobbin case - the spring lays across the **** in the bobbin case, through which the thread is pulled, so that the tip of the spring with a small right-angle bend just sits down into the aperture where the thread comes out. Now, importantly, the two screws are different sizes ... the one with the smallest head holds the spring onto the bobbin case and is screwed-down firmly through the hole in the flat end of the spring. The larger screw adjusts the thread tesnsion and is screwed through the hole with the slight conical sides. Now the tension should be adjusted to 5g using a proper gauge, but failing that, insert a bobbin loaded with a thread such as Metrosene and thread the bobbin case up. hold the end of the thread so that the bobbin case hangs on the thread - it should not move/unreel itself. If it does, adjust the tension screw (the bigger one) a little bit at a time until it doesn't unwind. The approximately correct tension is obtained when the bobbin will only unreel when you **** the thread upwards gently. You can fine adjust the tension to get the correct balance by ensuring the top tension is set to normal (red line) and adjusting the bobbin tension until the stitch lays properly in the fabric - use different colours top and bottom to check this. Be aware that the bobbin thread tension varies quite alot with only a small rotation of the adjusting screw, so take it is small steps.
Hope this helps.