You need the following information to link your account: Client ID, Client Secret, Slot id.
Client ID and Client Secret: You have to request both from MyTarget support team. Read about it in detail here: https://target.my.com/partners/help/reporting_api/.
Slot id: Go to APPS and then choose the app and the ad unit. Slot id is in Ad unit parameters and in the third column of the ad unit table.