If you are looking for the "++" content, your method of acquisition depends on your current ownership: Yo-kai Watch 4++
Yokai Watch 4 is an action-packed role-playing game developed by Level-5, where players take on the role of Keita (or alternatively, a female protagonist), a young boy tasked with exploring a fantastical world filled with Yokai, supernatural creatures from Japanese folklore. The game features an engaging storyline, improved graphics, and new Yokai to discover and befriend. yokai watch 4 purapura switch nsp jpn dlc up
Indicates the Japanese region version (no official English localization exists). If you are looking for the "++" content,