When you switch the shell from Bash to Zsh, the latter shell has no default dot file to obtain its PATH, so any UNIX command you run from the Terminal will state it cannot be found until you rectify a PATH solution.
Do you have a ~/.zshrc file in your home directory by opening a Finder window and pressing shift+cmd+. to toggle hidden dot files? Scroll down in that Finder window until you encounter the grayed out .zshrc file and then single-click on it and hit the space bar to display it with Finder's Quick Look. If the file exists, is there a PATH statement in it? If it does not exist. copy and paste the following in the Terminal, then press return.
<<"EOF" > ~/.zshrc
export PATH=".:/usr/local/bin:${PATH}"
PS1="%m: %~ %% "
EOF
That will write a .zshrc file in your home directory with PATH and PS1 shell prompt set. Then run this command:
source ~/.zshrc
and now, your current Terminal window knows your PATH, and UNIX commands should work now as they can be found.