Page Comparison

1. Click the Smart Guess button located under the Apps - button below the issue title:

2. Grant Smart Guess access to the required information

See article: Permissions Smart Guess requires

3. Once permissions have been granted

The app is displayed in the Jira issue and issue detail views, which means it is available where you need it:

Jira issue view

Jira issue detail view (a.k.a. issue glance)