To use the SOCKS5 protocol you simply need to specify that in the tool or language you are using it on, for example this is a curl using SOCKS5:
curl -U user:pass -x socks5h://gate.smartproxy.com:7000 ipinfo.io
The only difference between an HTTP curl is the
socks5h:// (mind the letter
h, as it specifies that hostnames are not resolved locally) added before the endpoint.
Note that you have to use gate.smartproxy.com endpoint in order to use SOCKS5, country endpoints like us.smartproxy.com will not work. You can instead target specific locations by specifying the location in your username using Single backconnect entry node, for example, this curl targets US location:
curl -U user-username-country-us:pass -x socks5h://gate.smartproxy.com:7000 ipinfo.io
Updated 10 days ago