Try You Tube? Honestly, if you try to fake a RP accent, you'll just get laughed at.
I'm personally not a fan of RP or of elevating it over other English language accents worldwide. In my opinion, it's artificial, classist and not a real accent.
Rather, if you feel people don't understand you when you speak, I would suggest you focus on improving your diction and articulation rather than changing your accent. For that, again, look on You Tube. There should be a lot of videos there to help you with that. Good luck.