Apply force using plectrum:
Apply force to the sides of the body using a plectrum.
Without opening the whole body, apply force to the plastic under the lens as much as enough to show the metal hook and its screw, get help if you can not keep the plastic bent.
IR filter Removal
I removed the filter some days ago so i can not post picture about this part but it's located at the bottom of the lens block, i had to crack mine, pay attention when cleaning lens to avoid scratches.
IR filter Reassembling
To reassemble lens block refer to the pivot used to set focus (marked white) located on the side of the lens block.