1. Boot the system
2. When it asks for a key interuption for interupting the boot sequence press any key.
3. This will give you ISL prompt.
4. Do a search for the devices. i.e SEA command.
5. Check which is a tape device (it will be mentioned as a Sequencial Device).
6. On the ISL Prompt give Command : BO (Tape device Name i.e. P1 , P2 etc.).
7. Press N for IPL.
8. It will boot from the tape.
9. Here you can select interactive or non-interactive recovery (this depends on if you have given options while creating the backup).  For a restore I used the non-interactive mode.

A menu appears. Choose "Install HP-UX". This will recover your system. If you are restoring to the same system you made the ignite tape from, you can use the non-interactive recovery. If you are restoring to a different system, it is best to use the advanced installation.