Hi @DT
I understand that you would like to give access to certain people to manage users in your Azure AD B2C tenant.
If you would like to give the access to new user, you can create a new user by choosing the Create a new internal user in your organization and fill the required information and assign required RBAC role to manage the users accounts.
I believe you are seeing the below error about access denied.
The reason you are seeing this error is because the user account is Local account which meant the user is not created in the directory, user has joined via user flow or guest.
However, you can assign RBAC roles to an existing user and manage the users accounts, to do this login to azure portal with your B2c tenant and search Microsoft Entra ID->Users->choose the required user and assign the least privileged role to manage the user accounts to know more about Least privileged roles by task
To manage your users in your tenant I suggest you create a new account in your b2c directory rather the existing users joined via user flow or guest user.
Hope this helps. Do let us know if you any further queries by responding in the comments section.
If this answers your query, do click Accept Answer
and Yes
for was this answer helpful. And, if you have any further query do let us know.