Is personnel in ISO 17025 required to have training and certificate before starting auditing the lab?

As for any management system activity, personnel must have suitable skills, adequate training and evidence of competency to perform a task.

Furthermore for internal auditing the auditors must be impartial and independent, meaning they cannot audit their own work and it is typically ineffective and risky if they audit processes their colleagues are responsible for. Internal auditors need not be certified auditors, but formal training is recommended, whether in house or through a service provider on site or remotely. Either way, management need to deem auditors suitable and competent through observation and against criteria such as professional approach, interview techniques, and outcome of an audit they performed under supervision. They need to have a good understanding of ISO 17025, risk-based thinking, the purpose of the quality management system and quality assurance activities. A technical auditor must, in addition, have a good technical working knowledge to audit the particular activity, including how to assess equipment, method validation, measurement uncertainty, calibration and metrological traceability needs.

The following ISO 17025 document templates may be of interest

Competence, Training and Awareness Procedure at https://advisera.com/17025academy/documentation/competence-training-and-awareness-procedure/
Internal Audit Procedure at https://advisera.com/17025academy/documentation/internal-audit-procedure/
Competence Approval and Authorization Record at https://advisera.com/17025academy/documentation/competence-approval-and-authorization-record/