Hi Paul -
Siewen was a village in the parish of Kruglanken, for which the duplicate
church
registers for the years 1834-74 have been filmed. These films are available
via
familysearch.org or the Sächsische Staatsarchiv.
The entry for the birth of Carl Conrad in Siewen is no. 93 of 1847 with date
20 May 1847,
so you should get quite far by perusing the films mentioned.
Best regards -
Bernd