If you have a disposable syringe, you can use it to suck up any large pools of liquid metal. Don't use the syringe containing your new liquid metal.

Starting with the heatsink: apply a few drops of highly-concentrated (greater than 90%) isopropyl alcohol to a cotton swab and carefully clean up all of the liquid metal from the heatsink surface.

Use the same cleaning process to thoroughly clean up all of the liquid metal residue.

Let the heatsink dry completely.