How can I replace the display?

Like you, I didn't find any written, iFixit-style guides for replacing the screen on your phone, sorry to say.

It is, however, very similar to many other Android phones in the basic procedure of how to replace your screen.

1. Remove the back
2. Unscrew and remove the midframe to access connectors.
3. Disconnect battery and fingerprint sensor.
4. Remove the battery.
5. Disconnect the display connector from the motherboard and peel it off the midframe.
6. Separate the screen from the midframe.
7. Clean the old adhesive.
8. Add glue to the edges of the midframe.
9. Secure the new screen.
10. Plug in the new display.
11. Install the battery.
12. Plug in the fingerprint sensor and battery.
13. Reinstall the midframe .
14. Glue the rear cover back on.

Although no written guides seem to be available, I did locate a YouTube video showing you the full procedure for replacing your screen.

https://www.youtube.com/watch?v=LCkyyO7U...

As you work, take lots of pictures then when you're done you can remedy the lack of a written guide by creating your own iFixit guide to BLU Vivo XI Plus Screen Replacement. It's easy, fun, and will gain you the appreciation of the repair community, especially those who come after you with the same problem.

https://www.ifixit.com/Guide/new/Device/...