It seems that some of the normals have been turned upside down.
After the full selection in Edit mode, it can be modified to Shift+N.
Please refer to the video and modify it.
but i want it to appear on both side
Making it render the backside is just a matter of turning off backface culling (Material properties > Settings > Surface).
But you should also want to keep a consistency of the Normals, and have them all pointing to the same direction.
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