public void UpdateDashboardItemCaption(
    string dashboardItemName
)

Public Sub UpdateDashboardItemCaption(
    dashboardItemName As String
)

using DevExpress.DashboardWin;
using System;
using System.Linq;

namespace CustomShowDataExample
{
    public partial class DesignerForm1 : DevExpress.XtraBars.Ribbon.RibbonForm
    {
        public DesignerForm1()
        {
            InitializeComponent();
            dashboardDesigner.CustomizeDashboardTitle += DashboardDesigner_CustomizeDashboardTitle;
            dashboardDesigner.LoadDashboard(@"..\..\Dashboards\dashboard1.xml");
        }

        #region #CustomizeDashboardTitle
        private void DashboardDesigner_CustomizeDashboardTitle(object sender, CustomizeDashboardTitleEventArgs e)
        {
            DevExpress.Data.IParameter showDataParameter = dashboardDesigner.Parameters.FirstOrDefault(p => p.Name == "ShowData");
            if (showDataParameter != null)
            {
                bool showData = (bool)showDataParameter.Value;
                DashboardToolbarItem showDataItem = new DashboardToolbarItem(showData, "Select states in the State list box and click this button to display data",
                    new Action<DashboardToolbarItemClickEventArgs>((args) => {
                        showDataParameter.Value = !showData;
                    }));
                showDataItem.Caption = "Show Data";
                showDataItem.SvgImage = svgImageCollection1[0];
                e.Items.Insert(0, showDataItem);
            }
        }
        #endregion #CustomizeDashboardTitle
    }
}

Imports DevExpress.DashboardWin
Imports System
Imports System.Linq

Namespace CustomShowDataExample
    Partial Public Class DesignerForm1
        Inherits DevExpress.XtraBars.Ribbon.RibbonForm

        Public Sub New()
            InitializeComponent()
            AddHandler dashboardDesigner.CustomizeDashboardTitle, AddressOf DashboardDesigner_CustomizeDashboardTitle
            dashboardDesigner.LoadDashboard("..\..\Dashboards\dashboard1.xml")
        End Sub

        #Region "#CustomizeDashboardTitle"
        Private Sub DashboardDesigner_CustomizeDashboardTitle(ByVal sender As Object, ByVal e As CustomizeDashboardTitleEventArgs)
            Dim showDataParameter As DevExpress.Data.IParameter = dashboardDesigner.Parameters.FirstOrDefault(Function(p) p.Name = "ShowData")
            If showDataParameter IsNot Nothing Then
                Dim showData As Boolean = DirectCast(showDataParameter.Value, Boolean)
                Dim showDataItem As DashboardToolbarItem = New DashboardToolbarItem(showData, "Select states in the State list box and click this button to display data", New Action(Of DashboardToolbarItemClickEventArgs)(Sub(args)
                    showDataParameter.Value = Not showData
                End Sub))
                showDataItem.Caption = "Show Data"
                showDataItem.SvgImage = svgImageCollection1(0)
                e.Items.Insert(0, showDataItem)
            End If
        End Sub
        #End Region ' #CustomizeDashboardTitle
    End Class
End Namespace

foreach (DashboardItem i in dashboardViewer.Dashboard.Items) {
    dashboardViewer.UpdateDashboardItemCaption(i.ComponentName);
}

For Each i As DashboardItem In dashboardViewer.Dashboard.Items
    dashboardViewer.UpdateDashboardItemCaption(i.ComponentName)
Next i