Depending on what happened you may find this is not something you want to try to fix.
If you dropped the camera then you have likely damaged some parts which will need to be replaced. Given the complexity and the special alignments needed you will not be able to bring this back to the same level of performance as it had when new. That is if you were able to replace the needed parts.
If you spills something onto the lens barrel you might be able to clean it off and get the camera working again. But without knowing what was spilled and where you may find this a hard fix as well.
OK, you'er going for it! What to do. First you'll need to get the repair manual for the camera look online for it otherwise you'll need to contact Canon. Next you'll need a set of tools like IFIXIT sells (the large tool kit). A good desk with a good lamp and steady hands. Good Luck!