i'm assuming it's still in the fermenter?
it simply might need more time. try warming it to 70-72 and rousing the yeast by gently lifting and swirling the carboy.
I would wait first. then go for the brett if it doesn't eventually get where you want.
In Process - Russian Imperial Stout, Nelson Sauvin Rye IPA, Mild No.3
In Kegs - Barley Wine, Apfelwein, Wild BlackBerry Wheat, Coffee Oatmeal Porter
Gone - so many :(