How do I use minor sequencer on Sorcerer?

Casters

It says in the spell description I use it with the special ability button, but it only shows special abilities my character has learned from resting and having nightmares. I'm playing Siege of Dragonspear.

Gallowglass

Cast the spell from memory, like any other spell. Keep that caster selected until the spell finishes casting, and then it'll offer you a selection screen to choose which two spells to place in the sequencer. (If the focus has been switched to a different character when casting finishes, the selection screen won't appear and the spell will be wasted.) Then a new special ability will appear, alongside the Bhaalspawn powers you gained in the dreams, accessed via the Special Abilities button.

Casters

I figured out the problem. After leveling I didn't rest, which is why I didn't see the spell in the list. Sorry.