Income tax return

Duirng FY2016-17 and 2017-18 I received Phd increment in my salary. But due to implementation of 7th pay where phd increment is removed, the amount given during the above period was deducted in the arrears amount paid to me in 2018 May. my question is that I have paid tax for the salary amount which include the phd increment and associated DA hike during 2016-17 and 2017-18. How to get back the tax paid extra during these financial years. As a governement employee, whether I should get new form 16 or how do deal with this.