I am unable to run Google assistant on my phone I am a citizen of India and want to run Google assistant on my phone. My phone is LS 4505 and Android marshmallow. Google app version is 8.0. And screen resolution 720p and 312 MB free space. So can I run Google assistant on my phone. And are there any other apps like this which I can run?
According to DeviceSpecifications.com, your Lyf Flame 8 (LS-4505) device has only 1GB of RAM and a 480p (480x854) display. It shipped with Lollipop, but further research indicates it was upgraded to Marshmallow.

According to 9to5Google, Google Assistant requires the device have Marshmallow or newer Android, 1.5GB of RAM, and a 720p display. Your device does not meet the minimum requirements to use this feature. 

As far as alternatives, a simple Google search will yield a variety of options, I did not investigate them to see if your device meets the requirement for any one specifically (this is not the Software Recommendations site), but you can start here doing your own research.