The Google Scripts Minecraft API provides two custom formulas to use within the Google Spreadsheet.
The GETIGN() function will return a players Minecraft IGN (in-game username) when the given argument is a UUID (Unique User Identification). A player's UUID can be found on sites like namemc.com.
GETIGN(uuid) -> username
Typing GETIGN("f5d5c301-9ad3-4cb4-9cfd-a6b78e67734a") in a cell will return Flashee. You can use the hyphenated UUID or the unhyphenated one.
An alternative to using namemc.com, you can use the GETUUID() function. It will return a players Minecraft UUID when the given argument is the username.
Because Minecraft allows for name changes, it is possible that a username could result in two UUIDs. By default, the function will return the current UUID attached to the username. To specify the date in which to check, simply add the date as the second argument.
GETUUID(username, date) -> uuid
Typing GETUUID("Flashee") in a cell will return f5d5c301-9ad3-4cb4-9cfd-a6b78e67734a. To specify a date, type GETUUID("Flashee", "7/21/2020"). This will check for the UUID of that username on that date.