Could try opening it up and resoldering in a new 4g slot if you can find one that's close enough on something else or the part. or wire in a sim breakout broad like this. Will look ugly but should work.
Please read these warning's.
I'd return it, or use it a as door stop or it's original firmware with a soldered in sim reader. it's not going to run OpenWRT routers that do are listed on.