diff --git a/nearby/README.md b/nearby/README.md
index 3801bfe..8451882 100644
--- a/nearby/README.md
+++ b/nearby/README.md
@@ -40,9 +40,9 @@
 1. Menu: File > Project Structure
 2. Select Modules at the left panel and select the Dependencies tab.
 3. Select the + icon and select 1 JARs or Directories option.
-4. Select the JAR file found above.
+4. Select the JAR file found above, make sure it is checked in the beginning square.
 5. Click the OK button.
-6. Restart the IDE to index.
+6. Restart the IDE to re-index.
 
 ## Build and Install
 
@@ -54,3 +54,23 @@
     --output /tmp/tethering.apex
 $ adb install -r /tmp/tethering.apex
 ```
+
+## Build and Install from tm-mainline-prod branch
+When build and flash the APEX from tm-mainline-prod, you may see the error below.
+```
+[INSTALL_FAILED_VERSION_DOWNGRADE: Downgrade of APEX package com.google.android.tethering is not allowed. Active version: 990090000 attempted: 339990000])
+```
+This is because the device is flashed with AOSP built from master or other branches, which has
+prebuilt APEX with higher version. We can use root access to replace the prebuilt APEX with the APEX
+built from tm-mainline-prod as below.
+1. adb root && adb remount; adb shell mount -orw,remount /system/apex
+2. cp tethering.next.apex com.google.android.tethering.apex
+3. adb push  com.google.android.tethering.apex  /system/apex/
+4. adb reboot
+After the steps above, the APEX can be reinstalled with adb install -r.
+(More APEX background can be found in https://source.android.com/docs/core/ota/apex#using-an-apex.)
+
+## Build APEX to support multiple platforms
+If you need to flash the APEX to different devices, Pixel 6, Pixel 7, or even devices from OEM, you
+can share the APEX by ```source build/envsetup.sh && lunch aosp_arm64-userdebug```. This can avoid
+ re-compiling for different targets.