I get that too. I first execute the command
export PATH="/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:/Users/username/Library/Python/3.7/bin"
And then esphome command.
This works for me. I struggle with “command not found” sometimes too. I don’t know anymore why I used this exact path, guess I googled it. I don’t use terminal a lot.
There are several sources on Google about Command not found for terminal commands.
EDIT: You probably have to install Esphome. The esptool is needed for running the dashboard locally, but you do have to have Esphome seperately installed. This can be done, on mac, with:
pip3 install esphome