You need the following information to link your account: OAuth-token, Page ID, App ID, API key (for SDK), Block ID.
OAuth-token: Read about getting an OAuth-token here: https://tech.yandex.ru/partner/.
Page ID: In Yandex Advertising Network go to Products, then proceed to Ads in apps where you should choose Mobile platforms. Page ID is located in brackets after the app’s name.
Application ID and API Key (for SDK): Via AppMetrica go to Applications tab and choose the app. In Settings you’ll see Application ID and API Key (for SDK) first in General settings.
Block ID: In Yandex Advertising Network go to Products → Ads in apps → Mobile RTB Blocks. In Formats you’ll find Block ID in brackets.