The default Agent role does not contain the Use Switch to Video permission. If you want all agents to have access to Switch to Video, you can edit the default role to contain this permission. Otherwise, if you want to grant this permission only to certain agents, you can create a custom role to apply to those agents.
By default, a newly created role has all its permissions unchecked. This prevents you from accidentally enabling unwanted permissions. Make sure to enable all the desired permissions for that role.