Q: fix seaching on iphone 6 ois 9.2.1

Did you already check this troubleshooting article?

If you can't connect to a cellular network or cellular data - Apple Support

SSearching no signal is common after a few faults.

• recent battery disconnect.  To solve this, connect phome to wifi and let it update its time/date. Then toggle airplane mode and your phone will find service
• Bent board. This one is a rabbit hole--the baseband of the phone has so many chips it is too open-ended to pursue at bird level
• water damage--same story. A "for the sake of the phone repair" after water damage is generally not worth it. Water weakems the solder joints all over the bboard, so even if you get the phone working now it may fail down the road.

AApple Is your best bet here. You can swap the phone as an out of warranty replacement for $299