Link the transitioned issue to the first issue mentioned in its description.
Add the Execute remote action post function to the desired transition or create a new transition.
Select the action Link an issue.
Choose an existing connection or create a new connection.
Set action parameters
Set it manually writing the following expression in the expression editor:
Relates
Choose Copy field value from current issue and select Issue key as field. The link will start from the issue for which the transition is performed.
Set it manually using the expression editor by entering the following expression:
%{first(findPattern(%{issue.description}, "[A-Z]{2,}-[0-9]+"))}
Optionally, you can use the Update issue fields (optional) section to save the response body or parts of it into some field.
Execute remote action