Sorry, I don't know how to bootstrap Certbot on your operating system!

I was having trouble with this as well since Amazon Linux 2 doesn't have epel-release in its repositories, but I've found you can install the EPEL RPM package itself, and then you'll be able to install certbot or certbot-nginx from there.

Download the RPM

curl -O http://dl.fedoraproject.org/pub/epel/epel-release-latest-7.noarch.rpm
Then install it

sudo yum install epel-release-latest-7.noarch.rpm
Now you can install certbot

sudo yum install certbot
And then run it as usual

sudo certbot
Check out the certbot page for configuration details after that.