How to add "sudo" group

I've done a mistake: I've removed the 'sudo' group, because I have forgotten the -a option (I wanted to add 'video' group):

sudo usermod -G video $USER

Now, when I want to call sudo I have this message:

orangepi@orangepi:~$ sudo apt-get update
[sudo] password for orangepi: 
Sorry, user orangepi is not allowed to execute '/usr/bin/apt-get update' as root on orangepi.

I read some solution (like visudo, or sudo adduser <username> sudo) but the problem persists. I can be root with calling su.

Some informations:

orangepi@orangepi:~$ groups
orangepi video               # I would like to add sudo, groupes and others

visudo:

Defaults        env_reset
Defaults        mail_badpass
Defaults        secure_path="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
root    ALL=(ALL:ALL) ALL

%admin ALL=(ALL) ALL

# Allow members of group sudo to execute any command
%sudo   ALL=(ALL:ALL) ALL

%shutdown ALL=(root) NOPASSWD: /usr/lib/arm-linux-gnueabihf/xfce4/xfsm-shutdown-helper

# Autoriser sudo ifup sans mot de passe
orangepi  ALL = (root) NOPASSWD: /sbin/ifup

How can I repair this?