Proposal Writers draft documents aimed at persuading the reader or recipient to either support a particular project or enter into a business agreement. Proposal Writers specialize primarily in grant and business proposals. Grant proposals convince readers to invest, lend or donate to a project. Business proposals persuade recipients to buy a product or service or to enter into a business relationship. However, a wide variety of industries can and do rely on proposal writers services, including health care, film, finance, and sports. A Proposal Writer must write factually and research thoroughly to convey accurate financial information persuasively.
Coming to the internship levels for the proposal writers, he/she can join any company as an intern and work with them for a certain range of months during their study period as the will get an hang on idea about their work and completed many internships based on content writing.
https://manipal.edu/mit/program-list/btech/btech-computer-science-engineering.html
etc. and many colleges in India offer writing courses.