Mercedes-Benz GLC 200 4MATIC Owner's Manual page 129

126 Seats and stowing
Press the seat belt tongue of seat belt
#
marked position 2.
1 In the rear: pull release lever 1.
into
#
To fold the left seat backrest forward: briefly
#
pull on left button 1.
The left seat backrest can be folded forwards
electrically only together with the centre seat
backrest.
If the left seat backrest is not engaged with
the centre seat backrest, this will be shown on
the driver's display.