How to pass ext RefNbr in issue to Journal Ext Ref

You just need to override the ReleaseDocProc method specified in the INReleaseProcess graph.

public class INReleaseProcessExt : PXGraphExtension<INReleaseProcess>
{
    public static bool IsActive() => true;

    #region PXOverride
    public delegate void ReleaseDocProcDelegate(JournalEntry je, INRegister doc, bool releaseFromHold = false);
    [PXOverride]
    public virtual void ReleaseDocProc(JournalEntry je, INRegister doc, bool releaseFromHold, ReleaseDocProcDelegate releaseDocProc)
    {
        releaseDocProc(je, doc, releaseFromHold);
        Batch batch = je.BatchModule.Current;
        if (batch != null && doc.DocType == INDocType.Issue)
        {
            batch.Description = doc.ExtRefNbr;
            //for extension fields need to get an extension class and then the fields
            je.BatchModule.Update(batch);
            je.Save.Press();
        }
    }
    #endregion
}

public class INReleaseProcessExt : PXGraphExtension<INReleaseProcess>
{
    public static bool IsActive() => true;

    #region PXOverride
    public delegate void ReleaseDocProcDelegate(JournalEntry je, INRegister doc, bool releaseFromHold = false);
    [PXOverride]
    public virtual void ReleaseDocProc(JournalEntry je, INRegister doc, bool releaseFromHold, ReleaseDocProcDelegate releaseDocProc)
    {
        releaseDocProc(je, doc, releaseFromHold);
        Batch batch = je.BatchModule.Current;
        if (batch != null && doc.DocType == INDocType.Issue)
        {
            batch.Description = doc.ExtRefNbr;
            //for extension fields need to get an extension class and then the fields
            je.BatchModule.Update(batch);
            je.Save.Press();
        }
    }
    #endregion
}

I try with your code “description field” has updated but extension fields not update. here is my code

public class INReleaseProcess_Extension : PXGraphExtension<INReleaseProcess>
{
    // Acuminator disable once PX1096 PXOverrideSignatureMismatch [Justification]
  public delegate void ReleaseDocProcDelegate(JournalEntry je, INRegister doc, bool releaseFromHold);
    [PXOverride]
  public void ReleaseDocProc(
  JournalEntry je,
  INRegister doc, bool releaseFromHold,
  INReleaseProcess_Extension.ReleaseDocProcDelegate baseMethod)
    {
        //je.RowInserted.AddHandler<Batch>(((cache, e) =>
        //{
        //    Batch glBatch = e.Row as Batch;
        //    BatchExt batch = PXCache<Batch>.GetExtension<BatchExt>(glBatch);
        //    batch.UsrExternalRefNbr = doc.ExtRefNbr;
        //    //je.BatchModule.Current.GetExtension<BatchExt>().UsrExternalRefNbr = doc.ExtRefNbr;
        //    //je.BatchModule.Current.Description = "test1";
        //}
        //));
        baseMethod(je, doc, releaseFromHold);
        Batch batch = je.BatchModule.Current;
        if (batch != null && doc.DocType == INDocType.Issue)
        {
            //batch.Description = doc.ExtRefNbr;
            BatchExt batchext = PXCache<Batch>.GetExtension<BatchExt>(batch);
            batchext.UsrExternalRefNbr = doc.ExtRefNbr;
            batch.Description = doc.ExtRefNbr.ToString();
            //for extension fields need to get an extension class and then the fields
            je.BatchModule.Update(batch);
            je.Save.Press();
        }
    }
}