If you do not attend your appointment, you must contact us within a certain amount of time. The notice we sent you inviting you to the appointment will tell you when you must contact us. Use this
Web form and tell us why you missed your appointment. If you do not contact us in time, we will close your application.
https://www.cic.gc.ca/english/helpcentre/answer.asp?qnum=786&top=5
Failure to appear for the Oath
Applicants are advised in the Notice to Appear to Take the Oath of Citizenship form [CIT 0024] that they must contact IRCC within 30 days of the appointment if they cannot attend. If the applicant provides a
reasonable explanation for why they are unable to attend, additional time may be given.
As described in
paragraph A13.2(1)(b), if the applicant fails to appear at the citizenship ceremony and does not provide a reasonable explanation within 30 days of the appointment, their application may be abandoned. In such a case, the applicant will have to reapply for citizenship.
https://www.canada.ca/en/immigration-refugees-citizenship/corporate/publications-manuals/operational-bulletins-manuals/canadian-citizenship/ceremony/oath.html