Most TP-Link routers is accessible using
admin credentials under one of these URLs:
Of course, you must try to access these URLs from the computer or mobile that is connected (via cable or Wi-Fi) to the same local network, your TP-Link router is connected to.
If above fails and you don't know current router's IP address, you may try accessing:
URLs from the same local network, your TP-Link router is connected to.
Most TP-Link routers registers a virtual URL (like above) and you can access their control panel even without knowing their actual IP address.