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Hi @vidyarathna
If it's from an old TPG customer, then this device has a special firmware that may not work in another country or SIM.
You may use this device as an access point or you may look for a technician to flash the firmware and install the default TP-link firmware.
BasilDV
@vidyarathna . Are you using this for 4G wireless internet or cabled NBN connection?
Do factory reset, login to router admin, check if there is a default username.
If it has tpg in it, you can try what the moderator says.
TP-Link website does have a firmware download available. The MR600 menu needs to have the firmware update function.