Can I do LEV testing myself or must it be done by a professional?

Trained employees can and should perform daily or weekly checks, such as checking airflow indicators, examining for obstructions, or listening for strange noises. However, a qualified individual must perform the obligatory LEV comprehensive examination and test. That implies a person who has the necessary education, tools, and expertise to assess performance accurately.
Not only is it dangerous to do it yourself without the proper knowledge, but it would also violate HSE's legal obligations. The official test must therefore be administered professionally, even though you can handle basic checks.