UART MP3 VOICE MODULE - sample code softwareserial.h not found

I am using Arduino 1.8.9. I am trying to compile the sample code from the wiki link (https://wiki.dfrobot.com/Voice_Module_S ... 4#target_6)
But I encountered the error:
Test_Voice_Module:17:28: error: SoftwareSerial.h: No such file or directory
compilation terminated.
exit status 1
SoftwareSerial.h: No such file or directory
I have tried:
1. To download SoftwareSerial.zip and added into the library but still not working.
2. Also read about NewSoftSerial but still couldn't get it to work.
Is there anyone kind enough to help, please?
But I encountered the error:
Test_Voice_Module:17:28: error: SoftwareSerial.h: No such file or directory
compilation terminated.
exit status 1
SoftwareSerial.h: No such file or directory
I have tried:
1. To download SoftwareSerial.zip and added into the library but still not working.
2. Also read about NewSoftSerial but still couldn't get it to work.
Is there anyone kind enough to help, please?