While the method above will work, using Content Creator Plus has the disadvantage that when the asset is openned it will be updated to whatever your build number is. This can result in errors being found due to a more rigorous error checking for later build versions, these you will need to correct so that the asset will show up in game.
It is better to use "Edit in explorer" then edit the config.txt file in a text editor such as Notepad. Finding the engine sound tag you can change the kuid reference to the kuid of the engine sound you want. You will also need to change the same kuid number in the kuid table that is in the config.txt file. After saving the modified config.txt file you will need to commit the asset.