Create a CSR , I find Digicert Util is the easiest way to do this

https://www.digicert.com/util/

Save the CSR request somewhere on a network available to the SBS server

Run this on the SBS server

certreq.exe -submit -attrib "CertificateTemplate:WebServer" %locationofcsrfiles%\csr.txt

Save to .cer file somewhere then import this into the server via the Digicert Util

Change the IIS Bindings to this nearly imported CERT