Aston Martin DB11 Owner's Handbook Manual page 74

Top Tether
The tether anchor point for the rear passenger seat is located
behind the top of the rear seats. The covers for the anchors are
embossed with the tether anchor symbol.
Push down on the front of the cover for the tether anchor to
release the spring clip.
3.28
Before Driving
Remove the cover for the tether anchor (B)
Engage the tether clip to the anchor point at the top of the parcel
shelf (C) and make sure that the locking spring has fully closed to
prevent accidental disengagement. Always make sure that the
tether strap length is adjusted to remove any slack.
To refit the cover for the tether anchor, insert the two tabs into
the slots. Push down on the front of the cover to lock.