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Hi @Tashi-2020 ,
Welcome to the community!
We have an existing article that you may find helpful, on this article they discussed information related ton how to change the Wireless Network Name and password please see link below.
https://community.tpg.com.au/t5/Broadband-Internet/How-to-change-wifi-password/m-p/604#M228.
Let us know should you require further assistance.
Cheers!