enable usb debugging in bootloop

Hi! hello every one.......I'm new to XDA ....
I m having yureka plus which I purchase 2 weeks before. I tried to root it but unfortunately it stacked in boot loop at yu logo. Now I want to flash custom ROM cm12 the computer is asking to enable USB debugging.
Can someone help me how to enabled USB debugging in boot loop.
Ur ASAP reply is highly appreciated.
Thanks in advance