Keep checking very regularly and even the day before itself but as others have said F redemptions to/from LAX are much harder to find these days.
The other option on the day is ask at the airport however I would imagine the price to an airport paid upgrade at the desk would be rather eye watering, one recently was $1589
https://www.flyertalk.com/forum/35655804-post874.html
CW home is still a great way to get back to the UK though and F out on the day flight and use of the CCR beforehand etc is definitely something to look forward to.
https://www.flyertalk.com/forum/brit...22-thread.html