Rpi4: Where to start?

[badrisuper]

RPi4 step-by-step set up: please help

I don't recommend to do so for now (updating OpenWrt in this case can be problematic), but if you really want to, just use any utility to edit partitions.... Since you mentioned you used unix, you should try to use growpart (https://www.systutorials.com/docs/linux/man/1-growpart/). Then do a resize2fs. Google is your friend

Here many forum members helped me to setup my Rpi4. Please check the above thread.

Badri M