Update Tab in an envelope c#

I have a number tab called Employee Number.  How do I update this tab using esign API in C# before I send the email?

This is my existing MakeEnvelope where I am attempting to do it:

        public static EnvelopeDefinition MakeEnvelope(
            string signerEmail,
            string signerName,
            string ccEmail,
            string ccName,
            string templateId)
        {
            // Data for this method
            // signerEmail
            // signerName
            // ccEmail
            // ccName
            // templateId
            EnvelopeDefinition env = new EnvelopeDefinition();
            env.TemplateId = templateId;

            //env.AllowMarkup = "false";
            //env.EnforceSignerVisibility = "true";
            //env.RecipientViewRequest

            Number employeeNumber = new Number
            {
                TabLabel = "Employee Number",
                Value = "1234567890"
            };

            Tabs tabs = new Tabs
            {
                NumberTabs = new List<Number> { employeeNumber }
            };

            TemplateRole signer1 = new TemplateRole();
            signer1.Email = signerEmail;
            signer1.Name = signerName;
            signer1.RoleName = "Employee";
            signer1.Tabs = tabs;

            //TemplateRole cc1 = new TemplateRole();
            //cc1.Email = ccEmail;
            //cc1.Name = ccName;
            //cc1.RoleName = "cc";

            //env.TemplateRoles = new List<TemplateRole> { signer1, cc1 };
            env.TemplateRoles = new List<TemplateRole> { signer1 };
            env.Status = "sent";
            return env;
            //ds-snippet-end:eSign9Step2
        }