The Convert Unix Time function converts Unix timestamps or Epoch time to UTC format . You can add an offset of your choice to account for time zone variance. You may search the list for a specific time zone offset (e.g., London) or you can enter a specific value (e.g., -2). Be sure to consider daylight savings times when you convert Unix time to UTC.
You can locate the Cleanup Unix Time function under the Tools menu at the top of your sheet, or by clicking on the ☰ menu icon in any column.
See this video for more information on Converting Unix Time in Gigasheet.