That other port is for Thunderbolt 2:
https://support.apple.com/kb/sp714?locale=en_US
Search for “Thunderbolt 2 to HDMI adapter” for options. Here’s one:
https://www.amazon.com/Plugable-DisplayPort-Supports-displays-3840x2160/dp/B00S0BWR2K
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That other port is for Thunderbolt 2:
https://support.apple.com/kb/sp714?locale=en_US
Search for “Thunderbolt 2 to HDMI adapter” for options. Here’s one:
https://www.amazon.com/Plugable-DisplayPort-Supports-displays-3840x2160/dp/B00S0BWR2K