Google Translate is deriving "Colonel" from 大佐, but 佐 by itself means "help" or "assistant."
It should be noted that the names of several other military positions also end in 佐, such as 中佐 (Lieutenant Colonel), 少佐 (Major), etc., with further distinctions as necessary for their position down the ladder and whether they are part of the army, navy, or air force. I presume the use of 佐 arose from such officer positions ultimately being assistant to the chief commander/general, but that's just speculation on my part.
The name 佐藤 itself dates back to the Heian period as a mutation of the name 藤原, with 佐 being used to notate the individual's position within the provincial government or the region where they lived; I've linked a great article about it below.
https://www.tofugu.com/japan/satou-japanese-name/