public void ChangeVersion( 
   VersionBase fromVersionBase,
   VersionBase toVersionBase
)

public void ChangeVersions(Geodatabase geodatabase, string toVersionName)
{
  using (VersionManager versionManager = geodatabase.GetVersionManager())
  {
   VersionBaseType versionBaseType = versionManager.GetCurrentVersionBaseType();

   if (versionBaseType == VersionBaseType.Version)
   {
     Version fromVersion = versionManager.GetCurrentVersion();
     Version toVersion = versionManager.GetVersion(toVersionName);
     
     // Switch between versions
     MapView.Active.Map.ChangeVersion(fromVersion,toVersion);
   }

   if (versionBaseType == VersionBaseType.HistoricalVersion)
   {
     HistoricalVersion fromHistoricalVersion = versionManager.GetCurrentHistoricalVersion();
     HistoricalVersion toHistoricalVersion = versionManager.GetHistoricalVersion(toVersionName);
     
     // Switch between historical versions
     MapView.Active.Map.ChangeVersion(fromHistoricalVersion, toHistoricalVersion);
   }

   // Switch from HistoricalVersion to Version and vice-versa 
   // MapView.Active.Map.ChangeVersion(fromHistoricalVersion, toVersion);
   // MapView.Active.Map.ChangeVersion(fromVersion, toHistoricalVersion);

  }
}

await QueuedTask.Run(() =>
{
  //Getting the current version name from the first feature layer of the map
  FeatureLayer flyr = MapView.Active.Map.GetLayersAsFlattenedList()
          .OfType<FeatureLayer>().FirstOrDefault();  //first feature layer
  Datastore dataStore = flyr.GetFeatureClass().GetDatastore();  //getting datasource
  Geodatabase geodatabase = dataStore as Geodatabase; //casting to Geodatabase
  if (geodatabase == null)
    return;

  VersionManager versionManager = geodatabase.GetVersionManager();
  ArcGIS.Core.Data.Version currentVersion = versionManager.GetCurrentVersion();

  //Getting all available versions except the current one
  IEnumerable<ArcGIS.Core.Data.Version> versions = versionManager.GetVersions()
          .Where(v => !v.GetName().Equals(currentVersion.GetName(), StringComparison.CurrentCultureIgnoreCase));

  //Assuming there is at least one other version we pick the first one from the list
  ArcGIS.Core.Data.Version toVersion = versions.FirstOrDefault();
  if (toVersion != null)
  {
    //Changing version
    MapView.Active.Map.ChangeVersion(currentVersion, toVersion);
  }
});