If using Lync / SfB, you can add the meeting room as a New Contact, or simply join a meeting using the Search facility.
To add a contact, go to Add a Contact, then Add a Contact Not in my Organization
Choose Other, then enter the room name that you'd like to add using this format: roomname@companyname.vc
Alternatively you can type the room name into the Search field, select the correct room and click Call on the right-hand side
Related Articles:
Microsoft Lync or Skype for Business
Regional Access Via H.323
Accessing Via Skype