HTC One M9 Plus

Hii, friends,
I have one HTC One M9 Plus phone bought from Malasia (Made in Taiwan printed on the box) and I have to write new imei to the phone immediately.

Could you please explain me how to write new imei without any special tool.
I did unlock the bootloader and also rooted now but telephone S-ON stage now.
What is the next step for writing imei using software only.

If some one explain the steps for writing new imei will be appreciated.

Thank you