You should leave PCB as it is, cleaning-resoldering can be done on the IC`s and affected terminals in the area.
If you really want a proper fix on that PCB, use chemicals to remove the soldering mask - i use DCM, applied after carefully masking surrounding area. I would not use sandpaper or any other tools to scratch it.
Then, the bare copper can be cleaned -i use chemicals again- and masked with soldering mask cured under UV.
Just my way to do it...