Topmusicanswers
Based on what you have written in your question I would suggest you just take it to a luthier. There are so many things you can get wrong here that it probably is not worth it. Widening the groove too far will lead to buzzing and tone problems and is not reversible - messing this up requires replacing the nut.
How can I widen my nut slots without files?
As for the nut, one quick way to widen the slots if you don't have special nut files is the use the bit of string you cut off from the locking tuners and use it as a file. Just run it through the corresponding slot to make it bigger. Go slow so you don't make the slot deeper, just wider.
How do you fix nut slot cut too low?
There are several ways to repair this issue. You can use dust or baking soda with glue, but I've found that a Q-Tip works very well too. You simply tape off the ends of the nut and then remove a small portion of the cloth and roll it up, then insert it into the slot that is too low.
