try this video:
http://youtu.be/vQ7K-l75I5M
presser feet
i assume it is like my 6600, in the back of the machine, behind the needle, is a lever, first,raise your foot, all the way up. next, there is lever attached to the accu feed foot, grab the accufeed and bring it out and down, under the foot you have attached already. once it is in place, it should work ...
you need to bring out your user manual.