I assume this is a miles ticket ? Hard to believe they would be this inflexible with a full fare F ticket.

Did they cancel the flight ? AFAIK LX does not oversell F, but I may be wrong.

As they contacted you > 4 weeks before the flight, unfortunately your options seem to be to accept the change or cancel the ticket and get your miles back.

Maybe check closer to the flight date as LX may release additional award seats on another flight to asia.