Workers are created automatically when the hash rate gets connected and there is no need to create them manually. Once you connect a miner with its worker name configured, the name will automatically appear in the device overview as a new worker. If you do not set a worker name in your device configuration, a new one will be automatically created with a name [auto] worker and your hash rate will be assigned to it.
Find instructions to how to connect your workers to the pool in Step 3 of the following articles:

Worker names are also case sensitive. For example, mining connections to workerName ABC, abc, and Abc are now treated as three independent workers. Just to remind you, a valid workerName (mirrored to pool workers) must match the following regular expression of characters "^[-a-zA-Z0-9_@+:]+$". If a workerName is not provided at all or doesn't match the regexp, the hash rate is accounted to the automatic worker called “[auto]”.