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Please make sure to apply mosaic censoring to the private parts.
Literal
Private-parts [to-に][topic-は] definitely mosaic [object-を] apply please.
局部 here means 'private parts/genitalia' — the same word that means 'localized area' or 'affected area' in medical/geographic contexts, with the body-part sense narrowed by the topic of censoring. モザイクをかける 'to apply mosaic (censoring)' — standard terminology for pixelation in Japanese media. 必ず 'without fail' emphasizes the requirement. A content moderation instruction.