In this activity there is a single profile (no trying to access someone else's profile here) and a bunch of requests to retrieve and modify the data.
I would recommend using software like Postman or RESTer to make different requests, learn the 'API' and then find the bugs. You can go a step further and also create automated tests as well!
Profile parameters:
The following POST requests are available along with an example JSON body. You will need to provide authentication with every request.
/setpassword/
{"newpassword":"YOURVALUE"}
/setbio/
{"bio":"YOURVALUE"}
/setprofile/
{"username":"YOURVALUE","bio":"YOURVALUE"}
GET https://www.r-adams.co.uk/apitestactivities/profile/get/
POST https://www.r-adams.co.uk/apitestactivities/profile/setbio/