'ion-title' is not a known element:

please help i get this error:
‘ion-title’ is not a known element:

Error: src/app/outlook/outlook.page.html:8:3 - error NG8001: ‘ion-header’ is not a known element:
[ng] 1. If ‘ion-header’ is an Angular component, then verify that it is part of this module.
[ng] 2. If ‘ion-header’ is a Web Component then add ‘CUSTOM_ELEMENTS_SCHEMA’ to the ‘@NgModule.schemas’ of this component to suppress this message.
[ng] 8
[ng] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
[ng] src/app/outlook/outlook.page.ts:5:16
[ng] 5 templateUrl: ‘./outlook.page.html’,
[ng] ~~~~~~~~~~~~~~~~~~~~~
[ng] Error occurs in the template of component OutlookPage.

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