Open the doors to let the fish out, vacuum the water out, then let it dry. If it was totally submerged, expect to be replacing computers and you'll be chasing corroded wire connectors for a long time. That will be much worse if it was salt water. Disconnect the battery until everything is dry. While it's disconnected, unplug any electrical connectors and check for water in them. You don't have to worry about anything underneath that can get rain water splashed on them. Electrical connectors under the hood have rubber seals that should keep them dry, but sometimes connectors inside the car are open to moisture damage.
You might consider setting a dehumidifier inside the car. If the water level didn't reach the pedals, there's good chance there won't be any serious damage.