I just received a corrected 1098. On my original box 5 was blank. On the corrected one, block 5 says $592.38. I have already filed my taxes, do I need to do anything?

It depends on whether or not you itemized or if you didn't itemized, how close you other itemized deductions were to the point of pushing your itemized deductions to be more than your Standard Deduction.

If your other Itemized Deductions didn't come close to your Standard Deduction, then do nothing - it won't help you any.

If you already itemized though, then this would decrease your taxable income by $600 or so, which would save you $600 times your marginal tax rate (say, $150 if you are in the 25% tax bracket). In this case, you might want to amend your return to collect the money - for information on how to amend your return, please see https://ttlc.intuit.com/replies/3288565

Note that PMI is not deductible for loans that originated prior to 2007