As Apple states
Important: Although both systems may use the same Apple ID for account validation, the iTunes Connect users and roles are separate from the Apple Developer Program membership and roles. A member of the Apple Developer Program for your organization doesn’t automatically have access to iTunes Connect. A member with an Admin role in the Apple Developer Program doesn’t automatically have an Admin role in iTunes Connect.
A team admin in iTunes Connect can add you as an iTunes Connect user so you can access the site.
From the above link:
To add a new iTunes Connect user
- As the team agent or other iTunes Connect user with an Admin role, sign in to iTunes Connect.
- On the iTunes Connect homepage, click Users and Roles.
- Click the plus sign. If it doesn’t appear, you don’t have access to create iTunes Connect users. The team agent, or an Admin user, needs to create the new user or update your roles to allow you to create new users.
- Enter the individual’s user information (first name, last name, and email address), and click Next.
The email address specified must be valid to activate the account. The user receives an email as a confirmation.
Review the email address of a user with an existing Apple ID.
If the email address you entered is already associated with an Apple ID, a warning message appears asking you to confirm that you want to associate this Apple ID with iTunes Connect.
Click Next to continue creating the user account with the existing email address and associated Apple ID.
Select the roles to assign to this user, and click Next
Roles give access to iTunes Connect sections. For example, the Admin role gives a user access to create and update material in all sections except Agreements, Tax, and Banking. The available roles are listed in User Roles.
Only the initial iTunes Connect user (the team agent) has access to the Legal role.
- Select the notification types assigned to this user by territory, and click Save.
- A confirmation line appears stating that verification email has been sent.
The new user receives an email from the iTunes Store that includes a link to activate the account. (Make sure to have the user check spam and junk mail filters if the activation email doesn’t arrive.)
If the account was created with an existing Apple ID, the user is asked to sign in to iTunes Connect.