is way too small to get a wrench or any type of tool in between and tighten the nut. Now what? Should i open the back of the guitar and try to fix it by myself?
If so, how will that look like? Never opened a guitar before. Or should i just take it to the luthier? (By the way, I don"t trust those guys. They always rip you off. If possible, I will rather fix it by myself.) Someone?