Actually a court of appeals cannot decide that.
A court of appeals can only decide whether or not the trial
court correctly followed procedures and existing legal precedence.
It is entirely possible for procedures and legal precedence to be
completely unfair (they have been many times) but if the trial
court properly followed them, the court of appeals must support the
trial court's decision.
If the court of appeals decides that the trial court failed to
follow procedures and/or existing legal precedent, then the case
must be retried in a trial court.