I don't like to use steel wool, but the usual advice is to use 0000 steel wool and oil to remove rust speckles.
My own preference is to use brass or copper wool (sold as pot scrubbers) and oil, since steel wool, even fine, can scratch bluing. Once the freckling is removed, degrease the surface and swab with cold blue. The brass/copper will stick in the rusted spots and the cold blue will darken it. (I like G96 Paste Blue, but any good cold blue will do the job.
Do NOT remove all the blue and reblue with cold blue. The result will NOT be permanent and the gun will look far worse than it does now.
Jim