Revelation 6:8

ἕστηκα is the first person singular perfect active indicative of the verb ἵστημι (histēmi), meaning "I cause to stand" or "I stand." The perfect tense in Greek indicates a completed action with a continuing state, which in English can be tricky to translate since there is often no sharp distinction between the present indicative and the perfect indicative when expressing a state.

Thus, ἕστηκα literally means:

"I have stood" (focusing on the completed action with present effect),
or in English, "I stand" (emphasizing the present result of having stood, vs. I am standing),
or more fully, "I have been standing" (which conveys the idea of a completed action with an ongoing present state).