If you are not able to access Mobile app channel in ACS than it might not be enabled for your instance and needs to be done but firstly depends on if you have a demo instance or referring to your organization`s instance.
Although, i have already seen the given links earlier and the only struggle is that i am unable to find the Adobe Campaign Standard portal from where i can configure my mobile application into adobe campaign to avail the push notification service.
Could you please help me to provide that link ? Does it require some access level permission in order to avail the same service.
For the reference, i have created my account on adobe portal and accessing Adobe Campaign using this link: Adobe Campaign
Here, i couldn't find option to achieve the "push notification" service. Although, it provide the links to the document's which you have provided in your reply earlier.