1. Observe and understand what the mistakes exactly are that they are making. Note the consequences. Understand what types of “mistakes” are high-impact versus low-impact. Be humble and approach with an open mind, there’s lots to learn about yourself and understanding what are mistakes with remedies and what are stylistic differences.
2. Offer assistance to the lead and do your best to make your team successful. A rising tide lifts all ships.
3. Make your career goals explicitly clear to your manager. Find ways to work together collaboratively to make your career successful and mutually beneficial there.
To reiterate — be humble. “No amount of coaching” has classically not been true in my experience. Usually what the case ends up being is that the organization has multi-layered problems and people are stuck in unsupported positions with less control than you might think. I don’t mean this in a derogatory way — I too started moving into tech lead roles with a similar mindset. Defeating that mindset is absolutely a prerequisite to being ready to be a true, good lead.