Setup JQL or Jira Board

Once the project is created, on project setting page user will get an option to 'Set up' Jira.

Click Setup under Jira
Selection the radio button for the required connection.
Enter the project key and use the slider button based on requirement to use Project Board or JQL.
Select the board from board dropdown or enter the JQL which is used in Jira for identifying a project issues.
Click Save button.

Edit Jira Configuration

Once tool is configured and user wishes to make changes to configuration then-

Navigate to Settings > Project > Edit Project
Click Edit configuration under Jira

Questions:

Once a Jira Board or Query is configured, is it allowded to change it ?

The option to choose between Board or JQL can only be done once for a Project configuration. If the option needs to change i.e. from Board to JQL or vice versa, a new project needs to be created.

What to do if after entering project key, no boards display on Boards dropdown?

If no boards are available, users are advised to check the Jira connection and ensure that valid connection is selected.

Can we use both Jira Board and Query into a project ?

No. Only one of them can be configured