C# Change baseAddress in app.config

`<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <startup>
    <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5" />
  </startup>
  <system.serviceModel>
    <services>
      <service name="IBSCommService.CommService" behaviorConfiguration="mexBehaviour">
        <endpoint address="IBSCommService" binding="basicHttpBinding" contract="IBSCommService.ICommService"></endpoint>
        <!--<endpoint address="IBSCommService" binding="netTcpBinding" contract="IBSCommService.ICommService"></endpoint>-->
        <endpoint address="mex" binding="mexHttpBinding" contract="IMetadataExchange"></endpoint>
        <host>
          <baseAddresses>
            <add baseAddress="http://ift.tt/1E89uPv"/>
            <!--<add baseAddress="net.tcp://localhost:8090/"/>-->
          </baseAddresses>
        </host>
      </service>
    </services>
    <behaviors>
      <serviceBehaviors>
        <behavior name="mexBehaviour">
          <serviceMetadata httpGetEnabled="true"/>
        </behavior>
      </serviceBehaviors>
    </behaviors>
  </system.serviceModel>
</configuration>`

I need to change the baseAddress using UI so that users can specify the baseAddress to use.

I have google alot, and cant seem to found a solution to access the baseAddress. Most are how to access keys in the app.config file.