My father-in-law put diesel in their 2009 honda crv. They drove approx. 2 mi. home. Now it won't start. How can I fix it?

How much diesel and how much gas is in the tank? If it's mostly diesel fuel (which I suspect it would be), drain the tank and refill with gas. Disconnect the fuel line at the engine, attach a piece of tubing and use the fuel pump to push the diesel out of the line into a container.

tenspeed is correct. My 17 year old daughter did the exact same thing. There is a lot of detail left out of the answer. My answer is more detailed, but it could be much longer. It is fixable but not without logistical challenges and expense like what to do with 12+ gallons of gas- contaminated diesel fuel. Will take the car to a mechanic tomorrow for a look over. We tried initially without purging the line which was simply not workable or efficient. 1) Remove fuel pump - challenging without the special tool to remove lock nut; 2) Siphon gas from tank - wipe tank with lent free cloth if you want to get several more ounces of diesel out; 3) reinstall pump - to get pump to go in easily, insert gasket, then insert pump into gasket; 4) add gallon or so of gasoline in tank (optional: added 1/2 can of injector cleaner); 5) detach fuel line under the hood - the fuel line can be determined by identifying the injectors and tracing it back from there, there are two places you can disconnect, if disconnected near fire wall (my choice), lower the fuel tube down and drain as much diesel out as possible; 6) purge line back to tank by holding a cup where the line is disconnected. Have someone turn the key to ON for about one second. This will get about 2 ounces of fuel out of the line. I did this 4 times. Twice may have been enough. 7) reconnect the fuel lines. 8) Crank on car. Took about a dozen attempts for the car to finally start. Coincidentally started right after I decided to put the air filter assembly back together thinking maybe it was getting too much air. Was using starter fuel in the intake. But don't really think it was helpful. Added another gallon or so of gasoline and remainder of injector cleaner. Will drive out as much of the fuel as I can prior to filling up. May use another can of injector cleaner for good measure.