Just practice imitating the desired accent a lot - eventually you will get really good at it. My perspective was growing up in southern England (Devon and Some

Just practice imitating the desired accent a lot - eventually you will get really good at it. My perspective was growing up in southern England (Devon and Somerset) and going to first public school and then private school (known as state and public schools in UK respectively). My Dad decided to send me to private school when I started developing a strong local Devon accent that he didn't like. At private school I learned "BBC english" that has a certain non-regional accent. For fun we used to imitate various regional accents - Devon, Somerset, London/cockney, Birmingham, Newcastle/Geordie, Yorkshire, Scottish, Irish are the main ones I remember. Later at age 23 I emigrated to USA and was immediately exposed to my boss's Brooklyn accent as well as generic NJ/east coast accent. Later moved to the midwest for 10 years and then the west coast, but by that time it was too late and I still retain what Americans consider a British accent, but which Brits now consider distinctly American.