Last year I missed a huge deduction somehow, I did a buy back when I refinanced my home in 2015! Can we correct this or try and use it this year?

If you missed a deduction on your 2016 tax return that applies to income earned in 2016 then you will need to file an amended 2016 tax return (Form 1040 X). The IRS information may be found here: https://www.irs.gov/newsroom/ten-facts-on-filing-an-amended-tax-return and the 1040 X instructions are found here: https://www.irs.gov/pub/irs-pdf/i1040x.pdf

You have 3 years in which to file the amendment. 

Also see the following: https://ttlc.intuit.com/questions/1908543-do-i-need-to-amend