Every since I migrated over to Maxis Fibre Internet, I have had constant WiFi and connectivity issue. Even I'm embarrassed to admit that I have a 10Mbps plan...

I have done plenty of research to custom router it but till date, I have no idea how.
Link either old or expired.

Just some info, I'm using this unifi modem model HG850a and I have Astro comes with my Maxis Fibre Internet.

Question, is it still possible to custom router it even though I have Astro subscription?
Help is greatly appreciated.