You will find a lot of courses for R programming but most of them are neither complete nor up-to-date. There are very few good quality courses and tutorials that are freely available.
Before you enroll in any course make sure it has the following topics covered:
Data manipulation
Data visualization and
Advanced analytics topics like regressions and data mining using RStudio
The above video will give you an idea about which topics must be covered in a course.
You can also check out the following free and end-to-end tutorial to help you decide among your choices
R Programming Tutorial | Learn R Programming | Intellipaat
If you also want a certification along with a course, you can check out the following complete course on Data Science with R.
Learn R Programming Online - R Programming Training Course
This R Programming for Data Science training course will help you be a master in data manipulation with R programming, data visualization and advanced analytics topics like regression and data mining using RStudio. During this course, you will work on real-life projects and assignments to master Data Science.