This question is in reference to Atlassian Documentation: Configuring a Board
Each board has a corresponding jql filter and shows the issues that match the filter. You can create a new saved filter - select it to match only issues from project XXX and epic with key YYY (e.g. project = "XXX" OR "Epic Link"="YYY") and from the board configure page you can change the board's jql filter - select the name of the newly created filter.
You must be a registered user to add a comment. If you've already registered, sign in. Otherwise, register and sign in.