There are some things that can happen to your compass that might make you ask, "Can I fix it?
If your compass has a bubble in it, it most likely still works. A bubble may be annoying, but it should not mess with the effectiveness of your compass. Bubbles are usually created by a dramatic change in pressure where the liquid compresses and the casing is slow to change. Usually, when you return to neutral pressure (or temperature), the bubble will disappear. If the bubble sticks around, try placing it in a warm environment such as direct sunlight. If this still doesn’t get rid of the problem, you may have a small leak in the casing that is allowing air to creep in.
A bubble in your compass is okay however, if your compass doesn’t point north, it is a problem. If your compass is failing to point to North a couple things may be affecting it. Check to make sure you are not near any electric lines. Electric lines tend to mess with magnetic fields and will cause your compass to point in a variety of different directions. Remember that your compass is made to point to MAGNETIC NORTH and not TRUE NORTH. Check what the declination should be for the area you are in.
If your compass is still not doing its job and pointing North, either take it to a specialist (which you can find online) or buy a new one. Don’t mess around and use a faulty compass.