Updating Zoom in the terminal

Zoom is not available in Ubuntu repositories. It also doesn't appear that the software can be installed via PPA, at least not officially, from the page you linked.

apt and your GUI software center only deal with packages that can be updated via sources in /etc/apt/sources.list or PPA sources or snaps.

There is a zoom-client snap in the snap store, but it appears that you did not originally install the software using this method, so you will need to follow the manual installation and update/upgrade instructions from the developer of the software via the link that you referenced.

If you have Zoom install by any way other than snap you must first uninstall. Try uninstalling via apt-get

sudo apt-get remove <zoom package name>

then you can reinstall it via snap. Do so either in Terminal:

sudo snap install zoom-client

or by use of the snap-store which can be installed with

sudo snap install snap-store

then updating all snap packages is done by

sudo snap refresh