I installed Debian on one plug on now I run it on another one. It works perfectly, but
mac address is wrong (seems it is assigned to the address of the previous device).
How to update mac address to the correct value?
You can set the MAC address either in the U-boot environment ("hardware) or in Debian "(software"). So it depends on what you have copied.
In Debian you would set it with a "hardware ether" line in the /etc/network/interfaces
Of course, it's also possible to hardware ARP table entries as well, so if none of this fixes things you'll need to expand on what you mean by "it is assigned to the address of the previous device").