Hi Devashree Seasons greetings The best way to Tirthan valley is to take bus from ISBT , Delhi .You can book HPRTC ( Himachal Pradesh state government buses ) through their Mobile application or website .There are different classes of buses available ( General to Multi axel )
You have to get down to Larji Tunnel and take local bus to reach Banjar ( Gateway to Tirthan valley )