City water and pump discharge connect to same plumbing system (cold water plumbing). Toilet water flows when using pump it ALSO will flow when using city water just like kitchen faucet, bathroom faucet, shower do.
No separate valve to swap for toilet.
Some RVs have a 'utility panel' where city water connects and valves/switches have to be changed to use: city water, use pump, fill fresh water tank, winterize etc.
But other than that panel the plumbing inside RV is same system.
So what did you try first......pump then city water?? OR city water then pump?
If pump then city water............did you try pump again?
Only thing I can think is city water pushed some debris/crud into toilet water valve clogging it. Basic RV water plumbing system (regardless of utility panel or not)