If your top is veneer, please do not sand your table. You could ruin it completely. Carefully remove the finish on the table top with one of the commercial products offered at the hardware or other stores. DO NOT let it drip on other parts of the table or you will end up having to redo the whole table. Your best advice will come from the store personnel who know "how to" restore your table.
You will have several other steps to this process to return your table to useable condition.
Really, the only thing you can do is to refinish the whole top. Sand it down good and reapply some polyurethane. Being the klutz that I am, I have now refinished my coffee table 3 times! LOL
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