Existing
noun, の adjective
Something that previously existed is probably still existing now.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
どれでもいいから、既存のファイルを開いてみてください。
Any of them are fine, so please open an existing file.
既存のデザインが突然変わったけど、これって何かのサイン？
The existing design just suddenly changed. Is this a sign of something?
ワニカニの既存のサービスに、追加機能が加えられる予定らしいよ！
It seems that additional features will be added to WaniKani's existing services!
しかも、既存のメンバーだけに特別な割引があるんだって。
What's more, I heard there's a special discount only for existing members.