Fix AWS Server - Security and SSL Issue

I have two separate issues on my AWS server. 1. The LetsEncrypt SSL certificate always fails to renew, so it throws a security warning when trying to access the website 2. Separately, AWS sent me an email about an abuse issue "The reported activity is the result of what is known as a reflection / amplification denial of service (DoS) attack. What this means is that certain ports (in this case, UDP Port 111) can be made to respond to a malicious request, with a lot of traffic being sent to the target of the DoS attack (in this case, Google IP addresses were the targets of the DoS, and your EC2 Instances were remotely used to DoS them). The vulnerability is caused by allowing *Inbound Traffic* from anywhere in the world (0.0.0.0/0) to all ports (0 - 65535) in your security groups configuration (which are attached to your EC2 Instances). To resolve this incident, please configure or firewall your server so it does not accept UDP requests to the listed port(111) from untrusted third parties. We have taken the following action against your instance(s) to prevent further abuse: ***Blocked UDP Port 111*** Reported Activity: DoS" At the moment, the website is down. Cannot access it