Hey there !

There are various online test series for OUAT. You can Google it and it'll show you the result. Various websites provide mock tests for OUAT, You can purchase them or few of them are free of cost. You can go for it !

Understand the pattern of the examination, make a suitable time table and strategy. Mostly the syllabus is based on NCERT so focus on NCERT particularly in case of chemistry and biology. Solve previous year question papers, also practice JEE or NEET questions as the pattern is quite same.

Practice as much as can, as practice makes a man perfect, keep focused and motivated. And Keep studying.

Good luck for your bright future !