how do I add a new accountant - I don't have the 'manage users' menu?

To add your new accountant, you must be the Primary Admin for your QuickBooks Online account. The reason there's no Manage Users under the cog icon is that you aren't signed in as one. To resolve this, either log in with the correct credentials or ask the current Primary Admin to invite the accountant directly. If you need to manage user access, the Primary Admin can transfer that role to you.

Let me know if you have further questions about managing your account.