Pestershum wont let me use a handle

[tumblryHugmaster]

Since I downloaded the client I wasnt able to make myself a handle. When I open it it lets me type one in and click the default mark, but after that it shows my handle as pesterClient[somenumber]. I am not able to chnage or switch it or anything.

Please help, I would love to proprerly use Pesterchum: (Sorry for errors or misspellings, I am not a native english speaker)