The distance to empty reading is based on a formula that the engine powertrain control module calculates with the message center. You can't really "reset" it; it's based on most recent fuel consumption verses mileage driven information, and averages it. Now, if you suddenly drive on a 400 mile highway road trip, that calculation will get lopsided in the opposite direction by the end of that hypothetical trip.
No cleaning or procedure you perform will change the DTE reading.
Now, for fuel economy - yes, make sure your air filter is clean. Make sure your spark plugs are good, and there is no misfiring. Be careful "cleaning" the MAF - many times this yields in actual damage rather than helping anything. I would bet that it is what it is...and there's nothing special to be done.