Securing your Trendnet router is not a tough task and requires you to follow few simple steps, which I will discuss in detail here. Going by your query it seems that your wifi is not even password protected which is a basic task to avoid intruders to get access to your personal network.
Step 1: First, connect your router to your computer or laptop using an ethernet cable ( yellow in color). Insert one end of the cable into your internet port of your Trendnet router and the other end of the cable goes into the ethernet port of the computer.
Wait for a few minutes to let the connection between the two devices get established.
Step 2: Open your browser and type in your IP address or the default IP address of your router web portal in the URL field and hit enter. In case you do not know either of the IP addresses, Google "My IP address" or "Trendnet default IP address" you will find the solution.
Step 3: Once you enter the IP address, you will be redirected to your router's login portal. Here, you need to enter your router login credentials provided by your Internet service provider.
In case you were not given any login credentials, you can use the default one to enter into router settings. The default username is "admin" and leaves the password field blank.
Step 4: Now once on the main settings page of your Trendnet router, click on "Advanced settings" from the side menu and then go to "Security settings". In the Security tab, change your encryption to WPA2 if it is not done so earlier.
WPA2 is considered to be a government graded encryption and thus one of the most secure options available.
Step 5: After the encryption, go to PSK or Pre-shared key, this is your wifi login password. The one you need to connect your device to your wifi. Now uncheck the invisibility box below and type in a strong password with a combination of uppercase, lowercase, and numerals.
Make sure that it is strong but at the same time something you can remember. Also, write it down somewhere in case you forget it. save the settings.
Step 6: By encrypting and creating a strong password your router is secure and can only be accessed by those who have the Pre-Shared key. If you want to make your router only visible to you and your devices, you can use MAC filtering option.
In this method, only those devices whose MAC address has been saved will be able to access your router. Go to "MAC address filtering" option from the settings and type in the MAC addresses of your device to which you want to grant access to your wifi and save the settings.
Now you have successfully secured your Trendnet router and only those devices with granted permission from your side will be able to access your Trendnet wifi router.
Hopefully, these steps helped you resolve the issue of Trendnet login. In case you have any difficulty in understanding any of the above-mentioned steps, kindly revert back to your query and I will be glad to help you out further.