Note: The below method will only work out successfully with MTK android devices, such as Tecno, Opsson, Gionee, Infinix, Lenovo e.t.c.
Now to get it done just follow the prescriptions below:-
►Download MTK Engineering Mode here
►Open the application and click on MTK settings
►Navigate to the right to "CONNECTIVITY"
►Select CDS information, and then Radio Information
►Now select either Phone 1 or Phone 2 depending on the sim IMEI you are willing to tweak.
►Click on the {AT }, about 4-6 option would pop-out, just choose either of the options bellow

Just select your preferred Sim:
►SIM 1:-AT+EGMR=1,7," "
►SIM 2:-AT+EGMR=1,10," "
►Put the IMEI you wish to tweak in-between the two quotation marks{"-"}
►Put a space between AT and EGMR.
►Make sure there is no space between the quotation marks and the IMEI number."123456789012345"
●►Now, tap the"Send AT Command"Option.

After taking all the above steps switch off your android phone and switch it on again. You have successfully tweak your phone IMEI.Enjoy.