In order to edit your campaign's target, you need to start from your All Ads page. Here you will see the list of all your AdSets; a button Edit Target is displayed next to each AdSet, just click on it to proceed.
If you wish to edit more than one AdSet, you can select one of them and you will be able to request a bulk edit directly at Step 2 of the target editing process.
You will be prompt with the edit form (Step 1) which reports all the targeting option currently applied to the AdSet. Here you will be able to edit your targeting preferences, then you can click on Proceed at the bottom of the page.
At Step 2, you will be asked if you wish to apply the changes made to the single AdSet you were editing, or all the AdSets that were having those settings (Bulk edit - Suggested option!).
Here I've added a CA to better define my target, and I surely want to apply it to all my AdSets that are currently splitted for placement as this is going to improve my target definition for all of them.
Click on one of the two choices, and you are done! :)