Bronica ETRS prism removal and metering

I received a Bronica ETRS, and the lens, shutter speed, aperture, mirror
release seem okay. I discovered after I bought it that the only thing
electronic is the leaf shutter stopping down. The attached prism has no
electronics. I think it is called the Prism E. (Foolish me; I thought E was
for electronic.) And there is no setting for film speed and no metering.

I am strictly limited to manual exposure photography, correct?

And I found that I could not remove the prism. The little release button on
the side depresses somewhat, but the prism will absolutely refuse to slide.
Any tips on that?

Loren