Follow the below steps:
1.Visit https://business.facebook.com/ and login with your existing Facebook account.
2. Choose your existing business page that you want to set up or set up a new business page.
3. Set up your account with additional account settings like team members, ad account and etc.
Also read-
How to add a partner/user in your Facebook business manager account
How to create LinkedIn ads account
How to add a user to your LinkedIn ads account
How to create Google ads account
How to add a partner/user in your Google ads account
