As already mentioned in previous posts, in order to install Burps CA certificate, just go to the IP address Burp is listening on, followed by /cert, e.g.
http://127.0.0.1:8080/cert. There you can download the cert and push it to your Android device. Usually you’ll get a binary certificate in DER format: cacert.crt.
Android won’t recognize this file as a cert. You’ll have to rename it to: cacert.der and push it to your device:
Afterwards you should be able to import your cert into your Android device.