How do you handle someone in the team who’s just said something I think is biased – but it’s not outright discriminatory and an HR issue?

Try to get them to reflect – ask them what they meant by that ; did you mean it to come out like that ; could you explain that joke? Often people will be able to work out for themselves after these kinds of questions that what they said was probably not well advised. Alternatively they may ‘double down’ on the bias as fact or harmless which makes it easier to address in terms of education or as a clearer case of discrimination.