How did Valjean liquidate the silver?

Someone like Jean Valjean.

I tell you thing or two about Jean Valjean. He's a criminal, with a criminal record, he know criminals.

You don't go to a pawn shop. You go to a friend of a friend who knows a guy who don't ask questions.

Also, there is an answer in your question. You know why you call it "liquidate"? It's from liquifing the stolen goods. You melt the gold and silver. Thus removing any resemblance to stolen plates and calderables.

In Père Goriot/Father Goriot (a story that took place in similar time as Les Mis) Honore de Balzac describe title character folding his silver plate into rolls to sell to jewelleres as "silver scrap" to not alert anyone as selling silver plates would rise questions.

Jean Valjean was able to just mash the silver into a pile and sell it as such.

I don't believe that any adaptation of the book (or the book itself) mentions this. However, there are always pawnshops and fences willing to take stolen goods from the hand of the thief, and Valjean, as a convict, would have easy access to them.

Eventually, since the priest officially said that he gave the stolen silver to Valjean, the thief could legally sell them getting more money than from a fence.