Help!!!ATT LG G3 have IMEI number, but unknown Baseband Version

My phone is unlocked. Currently I use Tmobile. After I restore my phone from backup from crash, my phone get signal from Tmobile like on and off. When I check about phone, I see I have IMEI number, but on Baseband Version, it shows unknown. Can you please help me to fix this issue? Thanks you!!!

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