Unfortunately I am not aware of a procedure, maybe some users are. The only workaround is to setup a custom weather with an outside temperature > 6C or to start at an airport which Live weather report a temperature >6C.
You should report it to Inibuild support since A350 is a 3rd party aircraft.
Existing reports for 1st party aircraft:
A320 - Engine failure immediately after startup under cold temperature condition
737 Max 8 Engine(s) Won't Start in Cold Conditions (< approx 6C) Following Checklist
FA/18 Can't start both engines cold & dark under low temperature
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