Mashing it on a tilted board with butter "pats" or paddles is my method. No cloth. You don't want to use something that will absorb the water and return it to the butter as soon as it comes in contact with it.
Without butter paddles, one can use a bench knife or scraper. With this process, one puts the butter on the tilted board over the sink then presses it firmly into a solid mass
Next cut all the way through it in parallel cuts right down to the board and press it again, scrape it up and rotate it 90 degrees, cut again press, cut, rotate and so on. This opens up the little pockets of water caught inside the butter.
Some people use a large butter board and a smaller cutting board to mash the butter mass.
The most important thing is to have the board tilted so the water can drain away.
The lady up the road who makes small batches of goat butter commercially uses the tempered glass cutting boards that have a textured surface and cuts and mashes the butter with dough scrapers
like this one