Setting static ip address in ubuntu server os

I am new to ubuntu server.
I am using rockpi4b-ubuntu-bionic-minimal-20190104_2101-gpt ubuntu server os in rock pi 4B v1.3.
I am trying to set static ip but /etc/netplan folder not available.
I tried sudo netplan generate also but showing error command not found.
anyone help me for setting static ip address.

Thanks
Vasu