Well the strategy is to work your way up from the local level because:

1. It's easier for people to make change at the local level, Fargo and St. Louis have already done it.

2. Politicians tend to work their way up the ladder, and will be more open to using the system at higher levels if they already proved they can win under that system.

You have to remember that any real social change takes years, even decades of organized to realize. We didn't go from Jim Crowe to the civil rights act in a fortnight, it took big organizations applying decades of pressure in multiple different ways.

If you want to be a part of the solution, join an organization dedicated to improving things. It doesn't have to be the one I linked, but Election Science is the one working on approval voting. Local elections are such that one highly motivated person can build and run the organization to flip their local election laws, it could be you, but it won't happen overnight.

As someone else pointed out, those in power are unlikely to change the voting system to reduce their own power. However, you really start at the local level with referendums, and work your way up. First, it's easier to force change at the local level and second, politicians working their way up will be less hostile to changing to approval if they've already shown they can win under that system.