I found these instructions on Pfaff Talk
, but I've never done it. I edited them to remove a discussion that is irrelevant to what you want to do:
To take the lid off the 7570
Unscrew the two philips screws, one in the thread basin, the other to the right and behind the bobbin winder. Do not touch the black screw that is part of the bobbin winder, as it has a very small washer underneath, which is likely to fall into the machine, and might do damage.
Now, push the bobbin winder to the right, just as for winding, and gently lift the whole top off. Now you can see the innards of the machine. To further help you, the left front cover can also be removed, and is only attached by a big black screw. Careful there, too, as it has a washer. Now you should be able to see the light, the needle threader, and the IDT.
When putting it all together again, don't forget to push the bobbin winder back to the left.