Issue list panel is placed on the bottom of the Session Dialog. It shows issues to estimate grouped by sprint.
Filters allow to hide issues that won't be estimated. They are not editable with the exception of the Session scope filter. To edit the session scope filter click the edit (pencil) icon, type a filter JQL and click "Save". The filter will be updated for everyone in the session.
If you are using next-gen boards you may find "Epic" issues in your issue list. If you would prefer not to see them there you can filter them out with a JQL query, like: