I wish I knew what I was doing, so help please.

I have acquired an old mirror, probably turn of the century, bevelled glass and a what I guess is a tongued mortise joint.

I'd like to fix it up and hang it on the wall above the oak dresser we just bought.
Is there a way to take the bow out of the original timber backing to the mirror? It has cupped badly as well and has a longish split, was 2 pieces.

It is about 900 * 500mm in mirror size and I cannot tell what sort of timber it is except that it is soft and a pale reddish colour, when made it was assembled with steel tacks an they have all rusted or corroded away.
It is at the Geelong Mens Shed at the moment so I can't get photos until next Wednesday.
I'd really like to restore or fix this piece, it must be worth a dollar or two, the local antique dealer offered me $30- for it last week