What have you tried so far, and what errors are you seeing?
# Optional proxy URL.
[ proxy_url: <string> ]
# Comma-separated string that can contain IPs, CIDR notation, domain names
# that should be excluded from proxying. IP and domain names can
# contain port numbers.
[ no_proxy: <string> ]
# Use proxy URL indicated by environment variables (HTTP_PROXY, https_proxy, HTTPs_PROXY, https_proxy, and no_proxy)
[ proxy_from_environment: <bool> | default: false ]
# Specifies headers to send to proxies during CONNECT requests.
[ proxy_connect_header:
[ <string>: [<secret>, ...] ] ] Exactly how you configure this depends on what sort of proxy you have, whether it requires authentication, and if so what kind.
You can find an example of proxy_connect_header here: