How do you fix your voice if you lose it?

Drink plenty of water. The best thing to do for your achy vocal chords is to drink water. Nothing on the entire Earth is better for you than good ol’ H2O. Keep it at room temperature to avoid shocking your throat with the freezing or burning liquid.
You shouldn’t be chugging the stuff like it’s your job. Your body is very good at telling you when you’re thirsty, so do not ignore it. Drink regularly, but sensibly. Not only will it help restore your voice, but it’s good for your body, your digestive system, your skin, your weight, your energy levels, and just about everything in between.

Gargle salt water. Four times a day, heat up a glass of water in the microwave (until it’s very warm, but not hot) and dissolve a tablespoon of salt in it. Gargle the entire thing. This helps deal with the mucus in your throat.
Don’t worry about the taste – you aren’t swallowing it. In fact, if your throat is a bit sore, you’ll probably find it comforting.
Another option is gurgling apple cider vinegar, although it is way worse tasting than salt water.

Consider drinking teas with honey and lemon. There are two sides to the story here: Some people believe that tea (especially chamomile with honey and lemon) is a great vocal soother. It’s been used for decades in this manner. However, know that acid is bad for your epithelial tissue (the stuff that makes up your vocal folds) and both tea and lemon are acidic.
There’s nothing wrong with honey, however. Another common (but less common) method is a spoonful of honey straight. What a great excuse to get your honey on! Next up they’ll be saying spoonfuls of Nutella.