My suggestion is not to put any more money in that machine. Since the timing is off for the second time, it's not likely to hold it for the long run.
What you are looking for is an adjustor's manual, not a user's manual. It will have the instructions for setting the timing. Also, do a search on youtube for the instructions (not the manual).
If you can't fix it yourself ,buy a vintage machine if your budget is limited. I prefer Singers from before 1970 because you can always find parts for them, plus the instructions are for fixing them are all over the internet.
JMHO
bk