Step 1. Go to the "Advanced settings" step.
You can access this step while creating or editing an action.
Step 2. Look for the "Product Back in Stock - make visible" section and then enable "Tag products that were made visible by Stockhide once their stock level has recovered".
Step 3. Start adding tags in the dropdown menu box.
Note that it can be a pre-made tag (you can choose from your list) or a new tag. You can also use multiple tags.
Now, the chosen tag will be automatically added to the products whenever it is made visible by Stockhide. The tag will also be automatically removed once the product is hidden.
Read more about Advanced settings.