How can we remove a subscriber from our Pushwoosh database?
For this purpose, we have /unregisterDevice API method which you can use knowing user's HWID. It could be called manually or directly from SDK.
However, in a case when you unregister device manually, if the app is still installed on the device, the user will be re-registered for push notifications next time he opens the app.
Also, GDPR Compliance feature allows a user to delete his data directly from his devices. This feature is available on Enterprise level accounts or as an add-on.