Cranberry sauce is usually served cold or chilled.
But if you want to heat the cranberry sauce up you can do so.
I like my cranberry sauce heated up so that it's warm but not too hot as it tastes better than being chilled or served cold.
However I do sometimes like to make cranberry sauce sandwiches by placing cold cranberry sauce out of the can onto some bread and eat it that way.
But when you eat cranberry sauce for Christmas or Thanksgiving dinner it's traditionally served cold or chilled but it's okay to eat it warmed up if that's the way you prefer it.