I ensure you that I don't have an "Accounting Firms" or an "Accountant" tab in my Manage Users sections. 

I further enquired about this through the QB Assistant and the info below is what was given. Through the method below I was able to send my accountant an invite. Not through the Accountant or Accounting Firms tab that I've been ensured is available on my account.

The instructions that I got from QB Assistant is as follows:

Adding your accountant is easy within Quickbooks Online!

1. Select the Settings  icon then Manage Users.
2. Select Add User and Company admin.
3. Check This user is my accountant. Note: This step doesn't apply to Simple Start subscriptions.
4. Select Next.
5. Enter the accountant's name and email address, then Save.

An invitation email will be sent to your accountant.

 Note: Your accountant must accept the email invitation within 24 hours, and follow the steps provided in the email to access your QuickBooks file.

I hope this helps anyone who was struggling like me to finally be able to invite their accountant.