The five steps of risk assessment were published by HSE precisely so that a sensible manager could apply them without specialist help: identify the hazards, decide who might be harmed, evaluate and control the risks, record the significant findings, review. For general health and safety a written record only becomes compulsory once you have five or more employees, though writing it down is good practice at any size.
Competence in this context is a proportionality test rather than a certificate. A duty holder who understands the activity, involves the people who do the work and follows the published guidance for their sector is usually competent to assess it. The failure mode is not amateurism; it is overconfidence, assessing risks whose mechanics you do not understand because the form looked simple.