How to Solve the Problem of "Remote Origin Already Exists"

Here is my situation: I want to use another GitHub account. I need to transfer a repo from my old account to the new one. Maybe there is an easy way to transfer, but it is beyond my ability now (I guess it’s complicated so I didn’t even bother searching for an answer).

So I git clone the repo from my old account and tried to push it to my new account. Then, a error …