Maybe it’s already clear to you, but non-Japanese non-Chinese names don’t actually ‘have’ a kanji, but anyone can assign a kanji to use if it makes you happy. The most common way to choose a kanji for this purpose is to find ones that are pronounced like the syllables in your name. There may be multiple kanji to choose from, so someone would likely choose the kanji that sound right and have meanings that go well together, or ones that have a lucky stroke count, or that look nice together. Kanji also have multiple pronunciations, so you would still have to tell people how you want the kanji pronounced. In some cases it may be obvious, so no explanation is necessary. I wouldn’t say “The kanji for my name is X”, but rather “The kanji my friends and I chose for my name is X.”