Mexican guitars are OK. Don’t worry. Setting intonation shouldn’t cost you anything. Use a tuner to tune each string then check it again at the octave. If it’s out of tune you have to adjust the bridge saddle to change the length of the string until the octave is in tune as well. (If it’s sharp you lengthen it) Use the screws at the back end of the bridge and take your time. It’s fiddly but not that difficult or risky. If that doesn’t sort it write again.