When I was young and poor*, a couple of times I bought part-worn tyres, and the tyre co provided them with the wheels because it was less trouble for them (presumably left by someone who'd converted to alloys).
You need a tyre fitting co to change tyres, they will charge for their trouble.
Remember that an impacted tyre might be damaged and might burst or deflate unexpectedly. This warning is always given but no-one believes it until it happens to them.
I had one deflate unexpectedly, luckily on the back of a mini, and the free replacement did the same, that's why I don't buy part-worns any more.
*I am now old and poor