Hi There!
This is a short code snippet to install Oh-My-Zsh on Amazon Linux.
TLDR
sudo yum update -y
sudo yum install -y zsh util-linux-user
sudo chsh -s /usr/bin/zsh $USER
sh -c "$(wget https://raw.githubusercontent.com/robbyrussell/oh-my-zsh/master/tools/install.sh -O -)"
# Now, disconnect and reconnect to the EC2 instance