You could try disassembling it, by separating those tabs at the sides with a small flat-bladed screwdriver,
but I fear parts inside might have melted or burned, which is what's most likely what will have happened to the fan resistor pack when it first does fail.
It's rare that it fails, but when it does, it's not unique to Renault in any way. I've seen it on other brands too.
If you can get a replacement from a breaker's yard or eBay, that'd be your best bet.
Doesn't need to be from another 172. Any Clio of the same generation as yours should be fine.