Often the go-to for various languages, including Swedish.
Since "Echo 3" is an original series, the most reliable and highest-quality Swedish subtitles are found directly within the Apple TV app. They provide professional translations that are perfectly synced to the video. Echo 3 undertexter Svenska S01E03
If you are looking for subtitle files (.srt) for other reasons, here are the most common community sources: Often the go-to for various languages, including Swedish