I would like to suggest the following corrections:
Dear Sir or Madam,
My name is Rebecca. I am twenty-three years old. I have been working as a bilingual receptionist for four years, but now I am looking for new challenges in my life. I studied English for several years in my childhood and since then I have always had confidence to communicate in English. I am a very patient and outgoing person. Being a receptionist, taught me how to handle in a high- pressure environment with calm and confidence. I also learned how to deal with different people and situations.
I truly want to make a career change and I believe I have the perfect skills to share my knowledge with others and to acquire new ones too.
I live in your school's neighborhood, so if you have a position for an English teacher, I am very interested. I have attached my resume for your consideration.
I’m looking forward to hearing from you.
I would like to make a few observations:
Don’t use contractions in a letter of presentation. If you are going to apply for a job in an English school it may sound a bit informal for someone who doesn’t know you. You don’t know who is going to read your letter. It could be a formal and strict person.
In this particular sentence you highlight that you studied English when you were a child and incredibly young (for me you are a young woman) but you didn’t mention if you kept studying over the years:
I studied English for several years in my childhood and teen years …. (a very confuse piece of information. When did you study? Did you stop studying English? )
If I were you I rewrite it:
I have been studying English since my childhood. I made several courses, including a ten-year course. I have never stopped studying the English language. Because of my work, I have daily contact with the language. For this reason, I speak English with a considerable amount of self-confidence.
Be careful with the use of commas in the English language. Perhaps this website can help you:https://owl.english.purdue.edu/owl/resource/607/02/
We NEVER write a profession in capital letter. Examples: I’m a doctor. I’m an engineer. I’m an English teacher. I’m a driver.
I'm truly willing to having a carreer change and I believe I have the skills to share my knowledge with others and to also acquire new ones.
Be particularly attentive to the spelling: career not carreer….
The grammar usage: I’m truly willing. It doesn’t sound natural English. A native would never use willing here but the verb want.
We use it when we want to say “eu estou disposta/ eu estou disposto”, but in this particular case, it may imply that you are making a “sacrifice” and you surely don’t want to convey that message in your letter.
I’m willing to sacrifice my career for it.
I’m willing to take a lesser job. (or a lesser position)
I’m willing to find a creative way to mitigate this burden…. (God knows what I have been going through…..
I’m willing to improve my English grammar…
I’m willing to take the risk…
I’m willing to change for you my love …
Don’t take my corrections quite seriously. They are just mere suggestions.
I wish you good luck in your interview!