Hi Claudia,
I think that you need to study the various pronouns -- Subject, Direct / Indirect object, Reflexive.
Your query relates to reflexive pronouns which match the subject "person" of which there are three -- I, you, him or her or it. singular and then the corresponding plural versions.
I recommend that you take each grammar element - understand, practise, test.
In time you will become familiar with the various aspects of the grammar and will be able to progress.
Bonne continuation.
Jim
