As discussed with canton team offline,
We can use
JAVA_TOOL_OPTIONS="-Dlogback.configurationFile=<my logback file>" daml sandbox
or
_JAVA_OPTIONS="-Dlogback.configurationFile=<my logback file>" daml sandbox
Thanks @Bas_van_Gijzel @samuel-williams-da1 and @Joao_Sa_Sousa for the fast reponse.