You can use the Etsy on Sale app if you like.
EtsyOnsale is a tool for sellers that can be used for adjusting prices and titles when they are having a sale.
You can find it (along with many other 3rd party apps) at
www.etsy.com/apps
Once you've decided what the discount should be, you simply tell EtsyOnSale and the changes will be made at the time you've scheduled your sale to start.
And the great thing is, it will change everything back once the sale is over as well.
if you want to give it a try for free you can use code
www.etsyonsale.com/sellers?referralCode=TQ2B0L32XI
Or you can use BETSI lite
https://www.etsy.com/apps/1660255685/1-free-bulk-listing-editor-betsi-liteI've not used BETSI lite myself but Graeme (the owner of the app) is extremely helpful if you have problems and the support is excellent