So you do have PLA, good!
To get functional TRAILER ASSIST you need to apply required coding/adaptations(see below) and your camera must be Compact+ (with optical ARA support).
Module 10
coding
Byte 3, tick Bit 3
Module 17
coding
Byte 12, tick Bit 5
Module 5F
Adaptions
adjust “ENG122229-ENG122332-Car_Function_List_BAP_Gen2-Trailer_Assistant_msg_bus_0x36” to “COMFORT BUS”
Module 6C
coding
Byte 10, tick Bit 3