Your IFSC code will be available in your passbook. Alternatively, you can also find your IFSC code through your bank's net banking website or through your bank's mobile application.
If the above methods are not working out for you, you can try finding your IFSC code on the following websites
1) https://www.rbi.org.in/Scripts/IFSCMICRDetails.aspx
2) https://www.policybazaar.com/ifsc/
If you enter a wrong IFSC code by mistake, your account details will not be validated and you will be able to enter the details again.