Some trackers make this hard, and a few have simply stopped working. Two things that usually help:
Check for a share or backup option rather than an export one — the file is sometimes offered through the iOS share sheet instead of a menu item.
Rebuild from what you can see. A spreadsheet with a date, a buy-in and a net per row is enough for Greenstack to import a complete history. Anything missing can be filled in later; nothing is required beyond a date and one money column.
Greenstack imports files from any tracker that exports CSV, including Bink, Poker Income, Poker Analytics and Left Pocket. Those names are used here only to say which files Greenstack can read; Greenstack is not affiliated with any of them.