Review Step 13 in this guide [guide|135320]
Are you sure the latch is missing? If it is you’ll need a new one. In any case the ribbon cable should still be removable if pulled gently out of the slot evenly and squarely. If not then someone may have used glue if you are sure you hadn’t lost the latch your self.
To replace the latch you’ll need to get a replacement connector to then transfer the latch to the one already present.