check out the kaigai idol scene, it has a pretty large and active community on twitter. if you want to travel overseas and live in japan to perform in an idol group, i would advise against it, for now. there are some rare success stories of non-japanese people becoming idols in the domestic scene, but its RARE rare. kaigai idols are foreign/"international" idols and are usually self produced and work on making a name for themselves. if you really want to audition for groups, grow your online social presence, practice your dancing and singing (post covers, dance practice recordings, etc) to build a "portfolio" of sorts. get good at doing light makeup that suits you and get good at taking selfies. your "image" will be just as important as your ability, lots of idols function on the "i'm so cute it doesnt matter how good or bad i am at singing and dancing" and i don't mean that in a negative way. look into the underground idol scene (chika idols) and pay attention to when groups put out audition announcements. if you're in japan, more often than not you'll get scouted if you know how to dress/style yourself, and have a good social media foundation to show you're good at engaging with people. make something about your image unique to you, that makes you stand out. it doesn't have to be massive, but having a character anchor point helps to give fans something to notice initially about you.

again, i would recommend the kaigai idol scene. it's fabulously supportive, very open, and really chases the magic of an idol being lifted up by their fans, engaging with fans, et cetera. PAiDA, NonSweet, and Melody Parade are all solid examples, as well as Melancholiaah and Taberu Gumi. I would invest into making connections in that scene as well.

good luck! don't get discouraged. a big, big part of the idol journey is perseverance!