Here is a short tutorial on how to decrease or change the range of your PLDT wifi signal.

Step 1: Login to your PLDT router panel 

Username: adminpldt

Password: 1234567890

Step 2: Click the "Setup" tab and click the "WLAN"

Step 3: Click the "Basic" tab and find the "Radio Power" attached is the screenshot

Step 4: Select the lowest percentage (I chose 10%) because I'm selfish. jk haha

Don't forget to click the "Apply Changes / Save Changes"

You may choose different percentage power depends on your need. The lower the percentage, the lower the signal range.

If you are using different Router, you may try to find Transmit Power/TX Power (I believed it is the equivalent of Radio Power)