Etsy has coupon codes that you can use to offer either a specific dollar amount or a percentage discount but they will be applied to the entire shop.
https://www.etsy.com/help/article/349?ref=help_search_resultIf you want to offer only a subset of your items for sale you can mark them down using Etsy On Sale
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