Parallel Web3 metaverses play a vital role in preventing monopolistic markets and fostering fair and profound user experiences. Meanwhile, ensuring interconnections and interoperability among these metaverses is crucial, allowing users to seamlessly transition between different Web3 environments while maintaining their digital identities and assets. In this tutorial paper, we provide an overview of the significance and current landscape of interoperability in parallel metaverses. Furthermore, we identify key challenges in achieving interoperability in parallel Web3 metaverses within the blockchain industry, including the technical complexities and practical business considerations. Then, we suggest that decentralized knowledge inference can be used as a potential solution for facilitating knowledge sharing among parallel metaverses. Finally, we outline the technical and economic approaches of decentralized knowledge inference to inspire future research in this field.