In GoAnywhere hover over the Tools menu and select the Manage SSL Certificates menu item. Select the Default Private Keys radio button and click on the Open button. Select the certificate that you want to have signed (or create one and then select it) and then click on the "Generate CSR" button. You will be asked to save it to your hard drive. This is the file you will need to send out to your certificate signing authority. When you receive a file back from your CA you will need to open the default trusted certificates again and import the signed certificate.