In some situations you might want to prefill some fields for the user. This can be achieved by the following method. 
Gleap.preFillForm(
    formData: <String, dynamic>{
        'description': 'This text will be prefilled.',
        'errordescription': 'This text will be prefilled as well.',
        'someformidentifier': 'This text will also be prefilled.',
      },
);
You need to pass a key value pair to the preFillMethod. The key is the form identifier, which can be found under the ‘Advanced’ section of a question. (see screenshot for an example) Form identifier