Hello Bao,
Thank you for contacting us. AdMob currently supports SDK-less mediation only for certain Ad networks (Aarki, CrossChannel, Drawbridge, Smaato). Firstly, you will need to link your app to the AdMob account and create a new Ad Unit ID. If you have already linked your app to the AdMob account, you will be able to setup the SDK-less Mediation by navigating to the Mediation group > Create Mediation Group > Ad Sources > Add Ad Network. You will be able to find the list of Ad Networks that support SDK-less mediation specified in the brackets.
Let me know if you have any other questions.
Regards,
Bharani Cherukuri
Mobile Ads SDK Team