This page will guide you explains how to configure existing associations in Jira and Salesforce.
...
The association configuration can be overridden by the Connection configuration. If a configuration does not show the expected behavior, verify that the respective setting on the Connection configuration is enabled.
Guide
Jira
In a Jira issue, look under the Salesforce section on the right side of the screen.
If you have the new Jira issue view enabled, click Associate or create a record.
If not, skip to Step 2.Choose the Association you would like to configure and then click Configure.
The Configure Association window pops up.
Set the desired options for the chosen Association and complete the change by clicking the Save button.
...
Open a Salesforce Object that has already been associated with a Jira Issue.
In the Salesforce Object, in the Jira Issues panel tiles/table view, click on the drop-down menu for the Association you would like to configure and choose Configure .
The Configure Association side panel pops up.
Set the desired options for the chosen Association and complete the change by clicking the Save button.