There is no radar for this one. The structure looks like this and can be found in the Blooming Plateau.

To spawn Jirachi, you will need the Melodic Tape. First go to the top and find this moss block. Break it and the one below it. You will see a barrel with the tape and some tera shards.

Use the Melodic Tape on the Jirachi Shrine. It will play the tape. Upon completion, the back wall will disappear and Jirachi will spawn.