I worked/used to work in restaurant business but now I want to improve my English skills and reach the level of proficiency, which I had when I graduated from the university, because I want to find a job that is nearer to my specialisation.

I worked in restaurant business, but now I want to reach the Advanced level in English proficiency again, which I was at while I was graduating from university. I want to work according to my speciality.

I used to work in a restaurant business, but right now I want to improve my English to the level that I had when I graduated from the university. I want to find a job according to my specialty.