You will need to find a person or store willing to purchase from you.
Then you will need an exporters license.
Exporting fruit and vegetables has been more stricter- Before any person could do so, now it has to follow proper procedure and not everyone can start exporting this. You have to do it properly, not " Dekha jae ga ". Due to amount of fruit flies.
From banks you will need " B " form to be filled out, they usually give a service like that for custom, tax; assessment etc.
Then your goods will be transported to the airport, remember this- Always and always send it via PIA Cargo. No middlemen that are standing outside and no " Waaqif " or " Chacha ka beta ". Most of the times, PIA cargo gives the lowest rates.
Our 753 kg shipment was sent 2 weeks ago, PIA cargo quoted 144PKR / kg, middlemen outside with a " Qanda " and a typewriter quoted 192PKR/kg.
I am not sure if this applies to mangoes as well, but get them checked from a laboratory for any diseases, fruit flies etc. and read on the rules and regulations for the country they will be imported to. Scan and forward the test results to them, hear what they say.
It's a fun business, but you have to be serious. Not all countries are forgiving.
Remember, the more kg you send, the cheaper it gets.
Enjoy 
Here's an image from Lahore Airport PIA Cargo section, mangoes from Hyderabad are going to the UK ( I think it was UK or either Saudi ).
