Why would HMRC assign two different UTRs?

My husband has two Unique Taxpayer Reference numbers - both received from HMRC via letter in August 2022. Why would HRMC send him two different Unique Taxpayer Reference numbers, and how do we combine them into one, please?

Hi faye_angharad,
If your husband as 2 UTR numbers for his individual Self Assessment he will need to contact HMRC to review and update to cancel the duplicate record.
Self Assessment: general enquiries
Thank you.