Hello Employer,
I understand that you want to implement the Coupons features on your existing products and for this you have bought an CSV files . As per my experience what you need is to implement the rules for the discounts on the products as per the CSV without conflicting the other rules on your existing store and for this you want to import the CSV on your store. Kindly, let me know if i have got the correct understanding of the job however, i also like to discuss the complete job in detail with you so, i can share relevant suggestions for this job along with an accurate time frame to complete it.
I am a Magento Certified Developer with more than 7 years of extensive experience in designing and developing more than 300+ magento stores, themes, plugins and extensions for my clients across the globe. I am also confident for the job as i have experienced with this kind of issue.
Looking forward in anticipation of your response.
Warm Regards,
Abhijeet