...
To link an issue in this way to a Salesforce object:
Go to a Jira issue you want to link to a Salesforce object.
Click on Edit.
The Remote Object Link field should be available for you to add a link (it may be named differently; you may need to ask your administrator if it isn't obvious).
It comprises of two fields for each object, a Salesforce object name and ID fields. The former is an auto-lookup field.
If you begin typing in here, it will actively search for the object in Salesforce and present you a suggestion list.
...
Select the object you want to link to from the list. This will auto-populate the ID field with the object's ID.
Click Save.
You should now see the Salesforce object's details in the issue details.
...