Go through your results for flights to Tarapoto in Peru with Netflights. The most popular airlines for this route are Iberia Airlines & LATAM, with Iberia Airlines claiming the top spot. Although KLM usually has the best prices, it's best to double check what's available for your travel dates.
If these flights are too expensive, try searching for a different time of year. So if your dates are flexible, consider looking at different times of year.
Tarapoto receives 15 direct and indirect flights every week, but the cheapest airline is normally KLM. So, if the flights to Tarapoto don't work for you, you could always try searching for flights to other airports in Peru.
Looking at a few different departure airports will give you even more choice. See what you can find. And remember, it's best to book your flights in advance wherever possible.