I usually take the "plus native plan" so it has been a while since I last took your lesson
I usually take the "plus native plan" lessons so that's why I haven't taken your lesson for a while
「普段はプラスネイティブプランを取っている」= I usually take the "plus native plan" / I usually take the "plus native plan" lessons
※「普段」= usually
「ので久し振りです」= so it has been a while since I last took your lesson / so that's why I haven't taken your lesson for a while
※「久し振り」はさまざまな英語表現になりますが、この場合では、「あなたのレッスンをしばらく取っていない」という事を表現したいから「 so that's why I haven't taken your lesson for a while」という英語になります。