It doesn't appear to have a name. Per the "original screenplay" book;
The steps appear to lead to a dead end: the doorway has been bricked up. Instead, a poster of a simpering debutante in evening dress, gazing at herself in a mirror, covers the end of the walkway.
TINA and QUEENIE stand in front of this poster. They turn to each
other and, in unison, raise their wands. As they do so, their work
clothes transform into stunning flapper party dresses. TINA looks up
at NEWT, somewhat embarrassed by her new attire. QUEENIE gazes at
JACOB, a cheeky smile on her face.
TINA steps towards the poster and slowly raises her hand. As she does
so, the eyes of the debutante move upwards, following her every move.
TINA knocks slowly on the door four times.
NEWT, sensing the need for a change, hastily magics himself a small
bow tie. JACOB looks on, jealously.
Possibly it's some sort of transfiguration spell.