Mimry Gardens
From The Pokemon Insurgence Wiki
To get to Mimry Gardens, you must first have obtained Meloetta's outside battle ability: Relic Song. Then you must proceed to the large, hollowed out, musical note statue in the southern-most section of Settlement Foxtrot. Then, after using Relic song on this statue a cave entrance will emerge. By following the newly found path, you will come out in Mimry Gardens. Then simply use the hiking boots to reach Delta Meloetta