『GENKI 1』Lesson 9 (6)┃ もう。。。ました (have already...), まだ。。。いません (have not yet)

You can use the affirmative past tense of a verb ～ました both to talk about an event that happened at a certain time in the past, just like did in English and also to talk about a past event that still has an effect at present, just like "have done" in English (used with adverbs like もう "already" for example). With the negative "have not yet...", まだ。。。ていません is used if your intention is to talk about how things stand now ("not yet").