My phone switching 5g to 4g then I on nr only my phone signal gone how to get only 5g network my dad phone has nr only model samsung galaxy a34 5g

My mobile restarting when I open any social media or game pls help me

Title: Galaxy A34 5G automatic random restartingDevice: Samsung Galaxy A34 5GProblem:My phone is automatically restarting randomly without any warning. Auto-restart option is OFF. The issue happens during normal use and sometimes when the phone is id...