Hi;
I personaly, have an OPPO BDP-93EU (BluRay Player) and as far as I remember to update firmware,
you have to switch off power, put in your "stick", and swtich on power again. May be, you have to push an other button (eject?) with the power-on button or meanwhile.
I'm not so sure, it' long ago, that I did that (because I have one with DVD Audio with ISO support).
Normally, OPPO supports SACD-R from "scratch" (original firmware)!
But at the other hand, are you sure, that your SACD-R is working well?
Make an ISO of them (may be with ImgBurn:
https://www.imgburn.com/) and put this ISO into Foobar2000 (with SACD components foo_input_sacd!)
and try to play back them. Look, if it works.
And do not mix up SACD-R with DSD-DISC, last is a specially Sony-format and with an other structure.
Try your luck ....