SD card for raspibian OS has two partitions /boot and /rootfs. Using SD card reader, I mounted the partitions onto my system with ubuntu OS.
For setting up static IP address edit the file dhcpcd.conf with root privileges.
$ sudo nano ~/rootfs/etc/dhcpcd.conf
Add the static IP details in the file.
static ip_address = 10.0.0.100
Save (Ctrl+x, Press y).
Since I was using headless setup ethernet cable connection between RPi and my laptop, I needed ssh to be enabled as default. To enable ssh, create an empty file named ssh in the /boot partition
$ cd /boot
$ touch ssh
Plug the SD card back to the raspberry pi board. Now the device (with username "pi", here) is accessible through ssh from the system.
$ sudo ssh firstname.lastname@example.org`
(My system was set with static IP of 10.0.0.200)
I found this example of how to do headless IP address setup for raspibian on raspberry pi with ubuntu in the following link. https://foolsvilla.blogspot.com/2020/03/how-to-set-static-ip-address-for.html . It worked for me.