Hi @Diana Piloya ,
The mailbox type in Online Exchange Admin Center is user mailbox. though would like the mailbox type in the on-premises exchange portal to switch from user to office365.
From the description, do you mean for some reason this user has mailbox in both Exchange Online and on-premises? If this describes your situation, it's recommended to follow the instructions provided in the article below to try correcting this.
How to recover when a mailbox exists in both Exchange Online and on-premises
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