Aljay on Family Tree Circles

Sievert was our great grandfather and emigrated to New Zealand through the port of Hamburg in 1872.I have been doing genealogy research for several years but have a brick wall that I need a hand to break down. We have his name on the passenger list for the ship Friedeburg sailing from Hamburg on 19 May 1872 and arriving at Lyttleton New Zealand 30 August 1872.The passenger record states he came from Tondern, His Oath of allegiance papers state he came from Slegvig Germany. We take it this would now be Schleswig-Holstein in Denmark. Any help to break down this brick wall so we can track the family further would be appreciated.

Regards, Laurie Jorgensen.