It's doable, you just need the debug version of the game which you should be able to find just by googling around, but I can probz find a link if you need one.
It's pretty easy to do yourself and there's very little risk of messing anything up (just keep a backup of your saves just in case). All you've got to do is open the game, go into the menu, select debug, variables (should be the second option from the top) and then scroll down to variable 0228, which will be labeled as "mysteryegg." Select it and then amend the number to 20, which I believe is the number for Rookidee.
Of course, if you want to do this the easier way, you can just use the debug menu to add Rookidee directly. Just open up the debug menu, scroll down until you find Rookidee, select it and then set its level as 1. It'll give you the option to put it in your PC or send a pokemon to the PC to make space for it, so there's nothing to worry about. It's super easy!