Hi Leah- I always use Etsy on Sale to run sales because it adds everything to all the titles you want, shows the discount, and then removes everything and puts the prices back to normal when you want the sale to end. You have to pay to use it if you don't have credits, but you can get 10 free credits when you first sign up with a referral link, which is enough to run two sales. My link is
https://www.etsyonsale.com/sellers?referralCode=4EI5TT454OIt's pretty handy and I have purchased more credits since I first signed up because it's so convenient. You can also use it to bulk edit tags or auto-renew items. Good luck!