Bechtle Help Centre.

A one-time drop off permission.
Setup a general drop off permission online.
You can easily set up a drop off permission online here. If you have already received a notification card, you can issue one-off or general drop off permission by using the back of the GLS notification card. Once the parcels have been dropped off in the agreed location, GLS no longer bears any liability for loss or damage to these parcels.  You can revoke the drop off permission at any time.
The GLS drop-off permission option may not be available in all countries.