New Holland Engine Power Derate

I am using a New Holland T5.120 tractor in Ethiopia and I have recently started receiving an engine power derate and DEF warning on the display. The warning first appeared the day before yesterday and has appeared again today. So far the tractor has only been checked by a local mechanic and I have not received any support from an authorised New Holland service or official customer service. At the moment there is no noticeable loss of power or other visible problem on the tractor, only the DEF and engine power derate warning is appearing. I am concerned that if this warning is ignored it may lead to a serious breakdown or expensive repair in the future. I kindly request technical guidance and clear instructions from New Holland on how this DEF and engine power derate problem can be correctly diagnosed and resolved, and what steps I should follow in my situation.