To Detach The Attachment Buckle From The Accessory; Example Of Optional Accessory Attachment - Sony FDR-X3000 Read This First Manual

Align the tripod screw hole in the bottom of the Underwater Housing with the tripod
1
screw of the attachment buckle, and fix firmly with the tripod screw.
Attach the attachment buckle to the accessory by sliding it until it clicks into place.
2

To detach the attachment buckle from the accessory

Press and hold the circled parts of the attachment buckle to unlock, then slide it in the opposite
direction of step 2.

Example of optional accessory attachment