I don´t see a Remote Button near the top of the iTunes window

Hi

The Remote button will only appear in iTunes after you have tapped on Add Device within the Remote app on Apple Watch. Note that your computer and watch must both be connected to the same Wi-Fi network.

In iTunes 12 and later, the Remote button is located towards the upper left, beneath the Volume slider. In iTunes 11 and earlier, the Remote button is in the upper-right, beneath the Search field.

More information:

Use Apple Watch as a remote control for iTunes or Apple TV - Apple Support

You're most welcome! 🙂

To clarify: the iPhone must be connected to the same Wi-Fi network as the computer, and your watch must be connected to your iPhone.

Although it is not relevant for this particular function, Apple Watch can in fact connect independently to a known 2.4GHz Wi-Fi network in order to provide certain functions (including using Siri and sending and receiving messages via iMessage) if your iPhone is not available.

More information:

Use Apple Watch without its paired iPhone - Apple Support