I'm looking for a course to improve my skills in marketing and teach me how to do business plan and marketing research. Can you please suggest me a course?

The best course for this is Chartered Institute of Marketing U.K,  which is  12 subjects program, which you have to go through  all pain of studying and preparining marketing and business plan. so one day you will be able to prepare Professional Business plan. Further you need to improve finance skills, so that  you could incorportae finace projection in the business plan. I would also say, CIMA stategic papers also  incoportaes this skills.  

You can join Ambeone Market research program. 
The next workshop is planned for 1^st to 3^rd April 2019.