Hello Azhar,
I assume you are running DB2 LUW and you have a valid back up.
You can either use command recover or manually call restore + rollforward to the end of logs.
Please check chapter 8.4 Database recovery of the DBA guide
http://service.sap.com/instguidesnw
-> your NW release
-> Database specific
-> Operations
SAP DBA Guide: IBM DB2 for LUW
Regards,
Javier