you mean, gym skill are included in migrated character who acquired it before the migration?
If your character has no problems after migration, just go to the 2nd floor of Eden Base and talk to the Gym NPC (the guy in black with shades, the very same npc on pRO) and choose the 3rd option if I not mistaken and it will be back.
If it has problems like DC and "fallen", your gym pass skill is lost and you need to report it here (or you can also file a ticket or both).