When you want to improve your Digimon stats with clones (available at Core Shop/Cash Shop), talk to the DATS commandant and choose the option you see.
Inside the cloning room, choose the stat you want to improve and click on "Digiclone", you must first make three successfull tries with clones D. When you are using clones C to A, there are less/more chances to fail and reduce the level of the statistic: in order to prevent that, when you choose the digiclone before clicking on "enchant", press "backup disk". If you do so, even if you made a wrong choice with the cards, you won't get penalty.
edit: sorry I was not logged. Digiclones can also be bought from cash shop