How to open a 17bii+ Silver?

[jebem]

I do not have that model, so I can't tell, but I'm curious to know more about it.

I do have a couple of HP-17BII, but these are using those four plastic rivets in the back under the battery cover and no screws are used. Basically these machines were not meant to be serviced.

But if you found two screws in the HP-17BII+, then it may belong to the new generation of Chinese made machines like the HP-35S.

Is your machine the silver color one using a similar body as the HP-35S?

If so, I would use a plastic pry tool to try to separate the two plastic cover parts (front and back). Force here should be contained in order to not break or dent any parts.
EDIT: But before doing this, please make sure there are no more screws under the bottom cover rubber feet (the 35S uses 4 screws, two at the top and two at the bottom).

See if this old link is of any use (but I guess that you found it before me).