You would need a Teflon foot. Which is a white plastic foot to help the leather easily move across the feed dogs the sit underneath the leather as you sew.
That said, the Bernina is limited in the thickness of leather in can handle and you would wand a decent thickness for your strap. The Bernina is also in need of serious service.
Without seeing the strap you are trying to replicate, I would say you can probably modify it and make a no sew version.
I don’t believe there are any riveting tools, I could be wrong. I always bring my own. You can get them quite cheap on Amazon. The size You would need would depend on the thickness o your leather. Of your leather was say 3mm thick You would want a 4/5mm long rivet.
Tools to the set the rivet. You get away with a hole punch rotary or manual, and a hammer to set it. You could get all the setting tools but then you may aswell buy a new strap.
Your welcome to borrow my tools to complete your project and I can send some links to some very good tutorials.
Similarly, you nèeded more guidance and anyone is interested in learning some basic leathercraft skills covering, riveting, cutting and sewing happy to run a session in the space if there is enough interest.
Hope something was helpful.