If you see a home you are interested in, you should first send a contact request to the landlord. If the landlord approves your request, a notification will be sent to you. Once you have been accepted, you can start to chat with the landlord and request to go on a viewing.
In other words, to arrange a viewing you and the landlord needs to agree on a date and time.
Make sure to ask as many questions as possible before the viewing. This will hopefully make sure that you don't go on viewings that doesn't accommodate your needs.