Looncan,
It's not quite as simple as just swapping 2 wires. There are 6 valid hall/phase wiring combos. 3 reverse and 3 forward. Invalid combos can also spin the wheel, and riding with an invalid combo can damage the motor or controller or both.
As long as the reverse is nice and smooth sounding (listen as it starts to spin), then it's most likely a valid reverse, and you will need to make a change to both the phase wires (the thicker 3) and the hall wires (the thin yellow/green/blue). Simply change 2 any 2 and only 2 phase (or hall) wires. Then find the correct combination of the 5 remaining hall wires (or phase if you swapped just 2 halls above). Use only small pulses of throttle when trying the different combos, and no it's not dangerous with only small pulses. Personally I use alligator clip wires on the phase wires till I find the right combo and just swap 2 of the halls. That way I know only low current is passing. When trying new combos only swap 2 at a time, which is easier and easier to be orderly.
This is the easiest method and guaranteed to work, so easy that I've done it with non-color coded wires and could do it blindfolded on a dare. Figuring out wiring combos is consistently the most common thing that many ES members over-complicate.
On many motors some combos can spin the motor, but aren't correct. IME these "false positives" are always in the opposite direction of the correct combo for a given hall or phase combo, and IME they sound rough compared to the correct combo. False positives will also have high current, so if you have a multimeter that can measure current it's always good to check no-load current once you think you have the right combo until you have more experience and can definitely tell the difference by the sound. If you can't measure current, another telltale sign is low torque, so if you try the bike and acceleration is very poor, then stop immediately so you don't damage the motor and go back to the 2nd paragraph above. Quite a few people have ridden their bikes that way and burned up motors or controllers.