According to the PMBOKGuide, the project manager is responsible for tailoring the project management processes and practices to suit the project context and environment. Therefore, the project manager should have assessed the organization's culture, performed a suitability analysis, and determined the future state before adopting an agile methodology. This would have helped to identify the readiness, gaps, and risks of implementing agile in the organization, and to plan for the necessary changes and support. Conducting agile training for all employees may be a good practice, but it is not sufficient to avoid the implementation failure.
Training alone does not guarantee the adoption or success of agile, as there may be other factors such as resistance, misalignment, or misunderstanding that hinder the agile transformation. Conducting a postmortem and capturing the learning in OPAs may be a useful activity, but it is not a preventive measure. It is a reactive action that occurs after the implementation failure, and it does not address the root causes or the solutions for the failure. Hired a third-party agile delivery team to do the implementation may not be the best option, as it may create dependency, communication, or integration issues. The project manager should have involved the internal project team and stakeholders in the agile implementation, and ensured that they have the skills, knowledge, and commitment to adopt agile. References: PMBOKGuide, Sixth Edition, Chapter 1, Section
1.2.4 (Tailoring) and Chapter 3, Section 3.2 (Project Management Process Groups)