Any pandy pretended :
The flat never came with a manual so I don't know how to change it. Anyone
got any idea?

Not sure what model it is but says nlvkbwhn on the back

Those I have come across, not Newlec, but it may be similar...

You need a key to open the unit up, to get access to the PCB. On the
PCB there are jumper pin links, 8 digits for a common code setting, 8
digits for a master code setting. If you know the present code, you
should be able to look at the jumpers, to see how the jumpers need to
be set.

The common code is the one given to all who might need entry and is
usually changed frequently. The master code is more of a static one,
for those who come less often, but still need to be able to gain entry
or for emergency use. I use one on my garage / workshop side door, to
avoid the need for keys.

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk