Before App Installing. follow these steps.

1. Go to Google Play Store. shown image below.

2. click on Menu Icon. shown icon under red line. see below

3. Open Link Play Protect

 4. click on these two green icon and stop scan. picture shown below.

5. after step 4 shown like this.

6. Go to Mobile setting and open safety & Privacy setting or Security Setting and find Unknown Source. see below

  

 

7. Now Install app. Thanks