In Version 2 (dont know about original versons.) but you must go to Floccest Town and go to the top of the town. Behind the school Alder introduced you to in the beginnig, there is a forest. Simply take Keldeo there, walkin front of the cracks in the big rock and it will forever go into Resolute form... Its prefered you teach it Secret Sword. Highly doubt it will work unless it knows its signature move.. Goodluck!