You can create a custom workflow and control your redirection parameters

Workflow for example - redirect to first child node under form page

 public class ChildThankYouPage : WorkflowType
{
    public ChildThankYouPage()
    {
        Name = "Child Thank You Page";
        Id = new Guid("4DE6729C-9808-4FFE-A668-8C67A0D98C6C");
        Description = "Redirect to child page with thank you message";
    }

    public override WorkflowExecutionStatus Execute(Record record, RecordEventArgs e)
    {
        try
        {
            var helper = new UmbracoHelper(UmbracoContext.Current);
            var page = helper.TypedContent(UmbracoContext.Current.PageId);
            var thankYouChild = page?.Children.FirstOrDefault();
            if (thankYouChild != null)
            {
                HttpContext.Current.Response.Redirect(thankYouChild.Url);
            }
        }
        catch (Exception ex)
        {
            LogHelper.Error<ChildThankYouPage>($"Workflow Error:", ex);
            return WorkflowExecutionStatus.Failed;
        }

        return WorkflowExecutionStatus.Completed;
    }

    public override List<Exception> ValidateSettings()
    {
        var exceptions = new List<Exception>();

        return exceptions;
    }
}

is working on a reply...