Thank you - the certificate confirms service with the Lichtenburg Commando (part of the 1st Mounted Brigade) in German South West Africa. Van Rensburg would have been entitled to a WWI trio of medals as well. His service card (not digitised) would be available from the SANDF Archives in Irene. Having only seen service in GSWA there is no personnel file.
Ask Dewald to draw this for you as well - he might not be aware of WWI service unless you inform him.