How to handle versioning with Git inside of JIRA?

I’m using JIRA 6.4.14 and Gitlab 11.6.0. I already have the integration setup between Gitlab and JIRA so mentions of the JIRA ticket number in a commit is posted in the JIRA ticket as a comment.

The process I’m having trouble grasping is that of versioning. For example, let’s say we have a quarter release cycle for our new software. And for the sake of the example, let’s say we’re at v1.1.0 and next quarter we’re going to release v1.2.0. During that quarter, we get as much work done as possible. Once we push to master and tag it as v1.2.0 (in Gitlab), how would I have all the JIRA tickets with that were fixed during that time be updated to reflect a label or something kind of release version of v1.2.0?

My goal is to be able to have an easy process to determine exactly what features and fixes are in v1.2.0 without having to go back and update each ticket.

Any advice?