Create a popup screen.

Add a label for the background, a label for message and two boutons, the group them.

Next set when to show the popup. in my case on InputBox onChange
UpdateContext({showDialog:true});

Set Cancel button OnSelect proerty to UpdateContext({showDialog:false});

Set Update button OnSelect proerty to UpdateContext({showDialog:true});

Last update the Visibile property for the Pupoup group to ShowDialog

To Add a record:
If no record found, patch.

//SubmitForm(frm)
Set(
    varRecord,
    LookUp(
        DocumentsCollectFeedbackValueStreams,
        Title = txt_Title_Value.Text
    )
);

If(
    IsBlank(varRecord.ID),
    Patch(
      DocumentsCollectFeedbackValueStreams,
      Defaults(DocumentsCollectFeedbackValueStreams),
      {
      Title: txt_Title_Value.Text
      }
  );
  Reset(txt_Title_Value);
  Set(showDialog, true)
)

To Update an existing record: