My system was 32 bit. I removed and re-installed Notepad++. After that from below got PluginManager_v1.4.12_UNI.zip and extracted it.
https://github.com/bruderstein/nppPluginManager/releases
I created a folder called PluginManager at C:\Program Files (x86)\Notepad++\plugins\ and copied PluginManager.dll into it. I restarted my notepad++ and now I see Plugin Manager.