My colleague has developed an APP before he left, his account has been deleted from the company.
Now I am going to maintain this APP, how I can get the admin access to it? I appreciate your help in advance.

My colleague has developed an APP before he left, his account has been deleted from the company.
Now I am going to maintain this APP, how I can get the admin access to it? I appreciate your help in advance.
Your Power Platform admins can give you access to the app as the owner from the Power Platform admin center. But you will also need access to the data source being used by the app. Depending on what that is you may need to get your Tenant Global admins involved.