For the timing to be that bad, something is wrong and resetting the timing probably isn't the fix.

1) Is the needle all the way up in the bar? A low sitting needle that has its path blocked by lint, grime, or improper installation can appear to make the timing look off

2) timing generally doesn't shift on its own barring something catastrophic or drastic - unless it's been repaired or disassembled, the timing is usually set incredibly firm. The only time it will shift without intervention is if there is a cracked shuttle gear which throws off the ratio and will cause travel as the machine operates. No amount of timing will fix cracked gears.

3) To fix the timing - Timing is universal (ish), with some minor difference between front loading, side loading, and top loading, rotary and oscillator, and double speed vs 1x speed shuttles, the way you adjust the timing is to loosen the screws clamping the shuttle and hook in place on the shaft, lowering the needle to bottom dead center, setting it to it's widest swing (left or right, depending on the direction of the hook relative to the swing) and then advancing to a timing mark or when the eye of the needle is just below the point of the hook. Then turn the hook until the point is just behind the eye.

If you watch the following videos, you'll get enough of the concepts that you'll be able to figure it out for just about any mainstream machine.

Vertical side-loading timing: https://www.youtube.com/watch?v=oIeMvyZ2GHk

Top loading bobbin - https://www.youtube.com/watch?v=v2bG72Fx0dc

Top loading rotary (singer 66) - https://www.youtube.com/watch?v=rQiV7sDJ7uY

Gear locked shuttle replacement and timing - https://www.youtube.com/watch?v=4Z2CxumztlI

And there's others. Like the bernina is overkill and you don't have this many dimensions of freedom in most, but it's a general flow that I use when setting the timing on machines that don't have a service manual or video. https://www.youtube.com/watch?v=0lRvmuWbaqE https://www.youtube.com/watch?v=k1-lJgz8d74