Please how do I reset a transaction pin on *600# to transfer airtime to someone

Hi Favour, before you can transfer credit for the first time, you have to change the PIN from the default PIN (which is 0000) to a new PIN via SMS or using USSD below:
Text: text 0000 New PIN New PIN and send to 777. Example: 0000 1234 1234 to 777
USSD: dial *777#, select to change pin, enter 0000 as your old pin, enter any 4 digit number you want as your new pin and follow the response.

If the pin is showing incorrect, you will need to contact MTN support for them to reset your PIN.

You can contact MTN Support via any of the channels below:
MyMTN App
Twitter: @MTN180 / @MTNNG
Facebook: @MTNLoaded
Instagram: @MTNNG
Live Chat: http://bit.ly/2OC5bHz
Email: customercareng@mtn.com
Call Center: 180 or +2348031000180 (if you are calling from abroad or another network)
WhatsApp: • 09033000001