The ./certbot-auto command is assuming certbot is in the current working directory. Do you know if you downloaded if before and placed certbot somewhere else? Try looking in your home folder for any directories where you may have downloaded certbot.
In addition to @jared.m's observation about figuring out what directory this tool was downloaded into, and the need to cd to that directory first, the correct form is ./certbot-auto renew, not ./certbot-auto --renew, which would be interpreted differently. However, this issue is not responsible for the error message that you saw; not being in the proper directory is the cause of that.
Edit: if you don't know what directory it was downloaded into, you could also try running locate certbot-auto, which might help you to figure that out.