You can go back and edit items after you’ve made them publicly available. Some changes may trigger a new version. Here's an article to find out which amends will generate a new version of your item.
You can also batch edit items that have already been published. In My Data, select the items to be updated, click on Actions at the top of the page, and select Edit in batch.
Once you’ve selected the items to be edited in bulk, select the metadata fields to edit. Custom metadata fields will be displayed here, as well.