What's your definition of a chess course? What books if any have you already read?
Without knowing anything besides your est rating I'd recommend studying middlegames and endgames. Start reading something like
Practical Chess Endings by Chernev and/or another PCE by GM Keres
A Guide to Chess Endings by Max Euwe
My System by Nimzovitch
Something by GM Kotov: Play Like A GM, Train Like A GM, or Think Like A GM
Many endgame principles frequently apply to middlegames and even openings sometimes so do not ignore endgame studies.
I'm roughly at 1800-2000 level and looking for chess course that suitable for my rating to became a master level. any recommendation?