What do I have to do to get my car started after having stalled in flooded road?

Start here:

https://www.2carpros.com/articles/car-cranks-but-wont-start

Get a helper disconnect a sparkplug wire or 2 and ground it to the engine atleast 3/16 away from ground-have helper crank engine over-do you have a snapping blue spark? If so-you have a fuel related problem, Do you hear the fuel pump come On when you turn key on? If not check fuel pump fuse and fuel pump relay if okay-check the fuel pressure to rule out the fuel filter/fuel pump/pressure regulator and listen to the injector/s are they pulsing or hook up a noid light. No snapping blue spark continue to troubleshoot the ignition system-power input to the coil/coil packs,coil's resistances,cap and rotor,distributor pick-up coil, ignition control module, cam and crank sensors and computer Note: If it doesn't apply disregard it and keep testing

It could be several things. Chances are the electronics got wet and need to dry. Check to see if there is spark to the plugs. Chances are there isn't. On the other hand, if the water was very deep and it sucked it in the intake, you need to remove the plugs, dry out the cylinders and make sure to change oil. NOTE: If that happened, the engine will most likely not turn over but rather be locked up.

Chances are good. My guess is that you soaked the crank sensor and it is shorting.

Glad to help. Let me know how you make out with it. If it doesn't work, we'll figure something else out.