Discalimer

/*
* Your warranty is now maybe void.
* We are not responsible for bricked devices, dead SD cards, thermonuclear
* war, or you getting fired because the alarm app failed. Please do some
* research if you have any concerns about features included in this ROM
* before flashing it! YOU are choosing to make these modifications, and if
* you point the finger at us for messing up your device, we will laugh at you. */

Required Files:

Procedure:

Need Good qcn or backup qcn from working phone using qpst. Dial *#*#717717#*#* to enable diag mode.
Run Software download from qpst nd there press backup to get yur qcn backup, Also you can restore qcn by same procedure.
(Note: Some times qcn backup and restore can solve yur unknwn baseband imei issues.)

Imei Repair and Imei Change:

* Required Root
* Need qcn backup
* Erase below givn partition from your phone
modemst1
modemst2
fsg

Example for Mi5 [Note: The partition block name will be diff in other phones] How to find partition block by name Guide here

adb shell su -c dd if=/dev/zero of=/dev/block/sde28
adb shell su -c dd if=/dev/zero of=/dev/block/sdf3
adb shell su -c dd if=/dev/zero of=/dev/block/sdf5
adb reboot

Imporatant: Note you should know the imei of backup qcn otherwise it vil be little hard to find. Now Open imei converter and there type your imei:
For Example: Assume this as yur imei 3558678954674546, 3558678954675684
Now Open imei converter and enter imei 1 by 1 to convert
After convert it vil be lik this 08 3A 55 68 87 59 64 47 45 , 08 3A 55 68 87 59 64 57 86
Open Qcn in Ultra edit, there use find option enter converted imei nd find the same line.

After find if you need to chnage yur imei from original change imei then convert using imei converter and replace it in the same line and save.

Restore using qpst.

For Efs Backup and Restore:

Backup:

adb shell su -c dd if=/dev/block/sde28 of=/sdcard/modemst1.img
adb shell su -c dd if=/dev/block/sdf3 of=/sdcard/modemst2.img
adb shell su -c dd if=/dev/block/sdf5 of=/sdcard/fsg.img

Restore:

adb shell su -c dd if/sdcard/modemst1.img of=/dev/block/sde28
adb shell su -c dd if/sdcard/modemst2.imgof=/dev/block/sdf3
adb shell su -c dd if/sdcard/fsg.img of=/dev/block/sdf5

For Network problem and unkwn baseband you can try this as well

Backup:

adb shell su -c dd if=/dev/block/sde28 of=/sdcard/modemst1.img
adb shell su -c dd if=/dev/block/sdf3 of=/sdcard/modemst2.img

Erase modemst1 and modemst2:

adb shell su -c dd if=/dev/zero of=/dev/block/sde28
adb shell su -c dd if=/dev/zero of=/dev/block/sdf3
adb reboot

Restore:

adb shell su -c dd if/sdcard/modemst1.img of=/dev/block/sde28
adb shell su -c dd if/sdcard/modemst2.imgof=/dev/block/sdf3
adb reboot