The ISO 17025:2017 clause on personnel is one of the most stringent in terms of mandatory requirements for a procedure and retaining records. The procedure must explain firstly how the personnel needs of the laboratory are determined (6.2.5a). Then the recruitment, training, supervision and authorisation process must be explained (6.2.5 b to e). You need evidence (records) for each step, including evidence of competence. Only once personnel have the required competence level, can they work on their own.