Sprue Safety Products WTSL-F-1EU Mode D'emploi Et Guide D'installation page 10

To make use of this feature you will need to push
out the two blanking plates on the top right-hand
side of the bracket, using a small screwdriver,
being careful to support the bracket fully whilst
doing so.
Once the rest of the installation is complete, and
the control unit is fixed to the bracket it can only
be removed using the following method:
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Insert a small screwdriver into the hole on the
top right-hand corner of the control unit, until it
stops, this will disengage the lock, then gently
ease the control unit up to release it from the
bracket.