Adding dictionary feature isn't working

Hi Metin, the 'Add to Dictionary' option you see, is a feature of your OS/device not your Microsoft SwiftKey Keyboard.

To add a word on SwiftKey, all you need to is tap the left hand or middle prediction (depending on text field) which will contain your verbatim text.

Here's more information: How does the Microsoft SwiftKey Prediction Bar work? – SwiftKey Support