Before proceeding toward next steps, first of a, l you have to make it sure that your Android mobile is rooted and Xposed framework is installed in your device. If these requirements are fulfilled by you, consequently, you can move on to further steps. This method can work on all android versions, even on Marshmallow (6.0+) device also. Hence, let's move on the steps.
You just need only one application named Mobile Uncle Tool on your android phone to change your phone's IMEI number. Therefore, you have to follow the below-given steps to change android IMEI number in an unrooted android mobile phone.