TLS 1.2 and TLS 1.3

Help!
1

run TLS 1.3 service from another in TLS 1.2, how is it configured?

2

What do you mean ? You want a frontend in TLS1.2 and a backend in TLS1.3?
This could be done this way:

frontend front1
    bind *:443 ssl crt /etc/haproxy/foobar.pem ssl-min-ver TLSv1.2
    use_backend back1

backend back1
    server srv1 1.2.3.4:443 ssl ssl-min-ver TLSv1.3