英语翻译“我曾经在韩国公司工作过.””在我工作的5年里,曾经换过3次工作.“英语怎么说?

I have worked in Korean company.
I changed my job for 3 times during the past 5 years.

I used to work in a Korean company.
I've changed my work for three times in the past five years.

I worked in a Korean company.
I have worked for five years and during these times, I changed my work three times.

I have had a job in a Korean company.
In my five years' career, I have changed my job for three times.

I once woked in a firm of Korea
During the five years of my since I worked,I have tried three jobs.