Welcome to the
Kitz forum.

I understand that the supplied Plusnet hub is just a repackaged BT HH5.
Assuming that you know the credentials for your Plusnet account, then if the Huawei HG633 allows itself to be reconfigured (either by its GUI or its CLI) it should be usable.
Never having used a Plusnet provided Internet service nor the Huawei HG633 modem/router I am uncertain as to what to advise. Perhaps you could try the simplest experiment by connecting a computer to the HG633, whilst the latter is disconnected from the line, and see if it can be configured via its GUI.