Getting this error:
E: The repository 'cdrom://elementary OS 5.1 hera - stable amd64 (20191202) bionic Release' does not have a Release file.
elementary OS Stack Exchange is a question and answer site for developers and users of elementary OS and applications. It only takes a minute to sign up.Sign up to join this community
It looks like you have enable your CD-rom as part of your sourcelist. You need to disable it.
Open the terminal and type (or copy/paste):
sudo nano '/etc/apt/sources.list'
It should look like this:
Set a # infront where it says deb cd-rom
So it looks like this: # deb cdrom:[elementary OS 5.1 hera - stable amd64 (20191202)]/ bionic contrib main non-free
Save: ctrl+o exit: ctrl+x
Now try again running the update:
sudo apt update