Tax treatment of joining bonus repaid in next financial year

Hi,

I received a joining bonus of amount X in March 2015. The Form 16 issued by the employer included this as my income and tax was deducted accordingly.

Now I would leave the company in September 2015 and according to my employment contract, I would need to return the joining bonus amount X to my employer. But tax on X has already been deducted during FY 2014-15.

What are the possible ways in which I can get back the income tax on X? Please do let me know your views on this. I'd be really grateful for your help.

Thanks,

Mish