I bought a second-hand router and I thought that restoring it to factory settings would eliminate the TP-LINK ID, but when I enter the Tether application it alerts me that the device is still associated with the previous user's TP-LINK ID. 

The question is: can I delete the TP-LINK ID of the previous user? 
I have written to the previous user of the router I bought but he does not remember the TP-LINK ID login details. I hope you can help me, thanks!