Reset ford fusion computer?

I'm presuming by "computer" You mean Your ECU, yes If so, the simplest way to reset the ECU is by removing the negative terminal cable from Your battery for about fifteen minutes. During this time, You should switch Your ignition key to the "on" position. This should do the trick. However, sometimes, that's a lot of hassle, when all You really want to do is wipe the ECU clean. Another way that avoids the battery altogether is locating the ECU fuse in the engine compartment's fuse box. You can determine which one it is by checking Your owner's manual, or an online diagram of Your specific model year. Disconnect this for the same period of time as above, and You should be off to the races.