If I received a sign-on bonus from company A, but I left the company before the agreed time causing me to repay the bonus. How do I report this to my tax ?

This is a claim of right repayment. You can only report it in the year you actually repaid the claim.

If your repayment is less than $3,000, you'll claim it as a Miscellaneous itemized deduction in Schedule A.

If the repayment is more than $3,000, please read this TurboTax Help topic on how to make the claim.