Thanks for asking question! There are few ways you can check deployment history.
• Kudu API shows a log for previous deployments in Json.
Access Kudu for your app service: https://[app_service_name].scm.azurewebsites.net
Click Deployments from Rest API section.
Direct link: https://[app_service_name]/api/deployments
It shows the list of previous deployments with most recent at the top. When you do have CI/CD set up correctly, it will shows commit hash, build and release IDs, so you can trace the deployment back to the pipeline entry/commit.
• You can go to your App Service, click 'Activity log' and set the timespan in which you think the deployment might have occurred (with a maximum of 90 days in the past)
• You may also View deployment history with Azure Resource Manager