It's quite easy to restore archived items.
If the item was recently archived, you can look for it in the workspace or collection activities. It will appear as a notification that looks like this:
To restore the item, click on the crossed-out name to be taken to the item. Click on three dots in the top right corner of the item name and click "Restore Item".
If an item was archived a while ago and you can't find it in the collection or workspace activities so easily, you can try searching for the item from your Profile Dialog.
Type in the name, or another defining characteristic, into the search bar. You can choose whether to search items or collections.
Click on the three-dot icon, then click "Restore Item" to restore it.