Simple steps to enable telnet on CentOS7

# you can first check if service already installed
rpm -qa | grep telnet

# install telnet service
yum install -y telnet-server telnet

# start and enable service at boot
systemctl start telnet.socket
systemctl enable telnet.socket

# if not yet installed firewall
yum install -y firewalld

# add rule to firewll to allow telnet
firewall-cmd --add-service=telnet --zone=public
firewall-cmd --add-service=telnet --zone=public --permanent

firewall-cmd --reload

# check if port telnet is opening/listening
lsof -i -P -n
firewall-cmd --list-all

# test locally
telnet localhost
# or test from other machine point to server ip
telnet IP_ADDRESS

# you might want to verify with other scanning tool like nmap
nmap -p 23 IP_ADDRESS

If you are on Windows client you can install git-bash or add “Telnet client” features