It's not clear if you were a regular W-2 employee or a 1099-Misc (or cash_ contract employee).
As a W-2 employee, the expenses would have been deductible in 2017 (but not 2018 and later, the tax law changed). You would have to file an amended 2017 tax return to claim that. But, For most people the real answer is: don't bother! You are allowed to deduct job expenses, subtracting what you were reimbursed (do not subtract your reimbursement if it was included on your W-2 as taxable income). TurboTax completes form 2106, which then carries to Misc itemized deductions on Schedule A. The problem with this is that you only get to deduct that portion of your misc deductions that exceed 2% of your AGI. and then only if your total itemized deductions exceed the standard deduction.
(2% rule explained: https://ttlc.intuit.com/questions/2902781-what-is-the-2-rule)
