Samsung — Phone auto restart problem

Respected sir,
Myself Ajay Verma from Mumbai maharashtra, m using Samsung galaxy m31 and the phone is already completed 13 months so my phone is not under warranty, my phone is auto restarting automatically, I had checked all my mobile settings no problem with the settings infact I already gone to Samsung service center also they updated my phone software, they said if the phone restarts again then u have to replace the motherboard and the cost of motherboard is 7 to 8 thousand, I can't afford it because m jobless from the last one year, my mobile no is [protected]

sir please give the solution for this, m belongs to a very poor family and I can't afford a new phone, please help me, waiting for your reply??