Help to change container interface MTU

I’m trying to change container awx-task interface MTU 1450 to 1400 but this keep getting this error:

[root@awx-7948bf7847-7zqwm ~]# ip link set dev eth0 mtu 1400
RTNETLINK answers: Operation not permitted

[root@awx-7948bf7847-7zqwm ~]# ifconfig eth0 mtu 1400
SIOCSIFMTU: Operation not permitted

I have to change MTU because is needed to sync with our intern gitlab…

How can I change this?

I installed AWX with k3s