能動態から受動態への入れ替えは、基本的には主語と目的語を入れ替えて、動詞をbe動詞+過去分詞にするとできると思います。

1.
この文はsvoo の第四文型なので2種類の答えがあり、
直接目的語を主語に取ると
This necklace was given to me by my uncle.
間接目的語を主語に取ると
I was given this necklace by my uncle.

2.
This room is not used by us now.

3.
She was named Harriet by her parents.

3.
Old DVDs are sold by them at that store.