You can open the Terminal from the side bar, or by pressing Ctrl+Alt+T. You can check what your default gateway is set to by typing route and pressing ↵ Enter. The address next to "default" shows your default gateway, and the interface it is assigned to is displayed on the right side of the table. If you have more than one default gateway set, you'll run into connection conflicts. Delete your existing default gateway if you intend to change it. Type sudo route delete default gw IP Address Adapter. For example, to delete the default gateway 10.0.2.2 on the eth0 adapter, type sudo route delete default gw 10.0.2.2 eth0. sudo route add default gw IP Address Adapter. For example, to change the default gateway of the eth0 adapter to 192.168.1.254, you would type sudo route add default gw 192.168.1.254 eth0. You'll be prompted for your user password in order to complete the command.

TL;DR in Vietnamese:
Mở ứng dụng Terminal. Xem cổng kết nối mặc định hiện hành. Xóa cổng kết nối mặc định hiện hành. Nhập lệnh .