How to handle negative influencers?

I have 3 employees on a team, 2 are in roles covered by the collective bargaining agreement, they have each been with the company 25+ years and have very poor attitudes, low performance and frankly should be terminated. The CBA prevents us from doing that. Meanwhile the third person is young, just out of school, and is heavily influenced by these two and has now taken on the attitude “I am going to do the minimum I can because I can”. This person has been asked to help another team because there is not enough work for his primary team, in the era of COVID most of us would say “gee thanks for any opportunity to be employed” but working with the two other employees has given him this sense of entitlement. HR and I met with him over zoom today to remind him he is supposed to be helping out this other team and he is not doing what is needed, he is not completing his tasks for team B. He had a bit of an attitude with HR which surprised me but I know this is his first job out of school and he only has the two bad apples as role models. HR didn’t want to write him up because he has a lot of potential and they couldn’t reference the other two team members for liability reasons so this is considered a verbal warning. What can I do to encourage him to fully engage with team B and his best chance of making it through the fall lay-off (he doesn’t know we will be having a staff reduction) is to do the things team B needs?