If you need to do this for hundreds of customers, then you should find a plugin, but..
If it’s just a handful of customers, you don’t really need a plugin, just go to WooCommerce > Customers and sort by Orders to see who has the most orders or sort by “Total Spent”, you can also export it to Excel if you want to run some calculations.
After that just go to Marketing > Coupons, generate some single use coupons, and email them to the customers.
If you need to do this for hundreds of customers, then you should find a plugin, but..
If it’s just a handful of customers, you don’t really need a plugin, just go to WooCommerce > Customers and sort by Orders to see who has the most orders or sort by “Total Spent”, you can also export it to Excel if you want to run some calculations.
After that just go to Marketing > Coupons, generate some single use coupons, and email them to the customers.
Some plugins to consider: [Conditional Coupons for WooCommerce](https://woocommerce.com/document/conditional-coupons-for-woocommerce/?aff=12943&cid=17113767), [Coupons Pro for WooCommerce](https://woocommerce.com/products/coupons-pro-for-woocommerce/?aff=12943&cid=17113767) and [Volume Discount Coupons](https://woocommerce.com/products/volume-discount-coupons/?aff=12943&cid=17113767)