"Seafarer" is not "wrong," but it is mostly a literary and even poetic word.  If a person were an explorer in the 15th through 19th centuries, such a person could easily be called a seafarer.  Christopher Columbus, Amerigo Vespucci, and Ferdinand Megellan were seafarers.  However, your post is about a modern navy or merchant marine, so you are better called a "sailor."

Since you are studying law, I hope this might be of interest to you:    https://www.saccourt.ca.gov/general/legal-glossaries/docs/russian-legal-glossary.pdf

<em>Here are some different ways to write this. </em>

Avon Ambulance

Thank you for your letter. I am a seafarer in capacity as a Chief officer with some duties as a Medical officer, and I have a medical care certification, and training to give first aid to vessel crew members. Frankly I have engineering qualifications and am currently studying law, but for me the medical sphere/field is very interesting. My grandma was a professional nurse and actually I grew up in a family with a medical background. I am keen on learning curve new fields/things of in life, like to knowing/learning new cultures, meeting people, and at the time I studying Japanese and online social learning courses.