In short: open ImageSEO → Bulk optimization in your WordPress dashboard and click Stop optimizer. The run stops and its queue is cleared. Images that were already processed keep their new alt text, titles, captions and file names. There’s no pause: to carry on later, start a new run.
Nothing is undone. Every image the optimizer finished before you stopped it keeps its new text and, if you had renaming switched on, its new file name. Images still waiting in the queue are left as they were.
Stopping clears the queue, so the next run starts from the beginning of your selection. To skip the images you’ve already done, set Optimize alt text to Optimize only missing ALT texts before you click Start optimization again. If you choose Optimize all ALT texts, every selected image is processed again and counts toward your monthly images again.
The full walkthrough of the settings is in how to bulk optimize your images.