The parish Lamstedt is part of the Kirchenkreis (church district) Cuxhaven-Hadeln of the Hannoversche Landeskirche (state church of Hannover.
The parish records of the Kirchenkreis (church district) Cuxhaven-Hadeln are not online on archion.de until now.
To get information where the churchbooks are stored you should ask the church office, as Helmut suggested.
Sometimes they are stored in the parish office but very often in the church district office.
You can write to Ev.-luth. Kirchengemeinde Lamstedt - Kirchenbüro - Feldstraße 5a, 21769 Lamstedt or send an e-mail to KG.Lamstedt(at)evlka.de.
Lamstedt was Lutheran, so Archion would be the place to start. If their church books are not yet online one would have to ask the parish office where their records are held.