Solution is now on the wiki: Get Started with T1000-E Tracker | Seeed Studio Wiki
You will need to reflash the bootloader, flash the erase flash file (to clear the flash) then flash the meshtastic file.
Also, for newer firmware the DFU mode is not the double click anymore, but hold the button and the connect USB and the disconnect and reconnect it and then release the button. Just rock the connector off to the side and then let the magnet snap it back on. The Part 2 video on the page shows the steps at 112 seconds (1:52) SenseCAP T1000-E Meshtastic Tracker User Guide - Part 2: Status Indicators of the T1000-E
When I installed the adafruit flasher via pip with --user as in the instruction, it didn’t work. I think there was a path error so I reinstalled it without the user from a windows admin cmd/terminal and it worked then.