It is seen in Micromax and other MTK phones when flashing/Updating Rom then we are lost your IMEI No, This is a big problem for new Micromax phone users. So, I give you the solution of this problem. It is simple but do careful. have a look ....
Write lost IMEI No or Change your phone IMEI No by follow method :-

Must Read :- How to Backup/Restore of Androidphone IMEI No for MTK device

1. Go to Engineering Mode with this code * # * # 3646633 # * # *
2. Type it on call pad
3. Then Engineering Mode show on your phone screen
4. Go to  CDS info
5. Go to  Radio info
6. then go to  Phone1 (For the first IMEI No)
7. At the top there is a command line which begins "AT+" just type there "AT +EGMR=1,7,"IMEI_1" (Instead of IMEI_1 put your first IMEI No)
8. Hit send command
9. If you done just reboot the phone
10. If you change the second IMEI No then go to step 2 and select "Phone2"
11. And enter the code "AT +EGMR=1,10,"IMEI_2" (Instead of IMEI_2 put your second IMEI No)
12. Hit send command
13. Reboot your phone

That's all now we Writes lost IMEI No and Change your IMEI No. But once again i tell you that First read all steps then do it careful.