Instead of changing legacy code its always better to create a new legacy code. Its not that hard, once code is pushed to git it becomes legacy.

Ask some major questions to yourself first 1. Have you well clearly informed to your team member in advance about the legacy scope of work prior to considering him/her into the team?. 2. Have you discussed the expectations and vision of the team member in advance about the legacy scope of work prior to considering him/her into the team?. Is it well aligned to take up a legacy software task?. 3. Do you have the documented Teeny-tiny details and all required information of the legacy work to be taken up?. If any of the answer for the above mentioned questions is a "NO" then it is 100% the assigner (Management/leadership/lead or whoever) responsibility is to admit the mistake and move on by correcting it than torturing an ambitious person.

The best way to deal with pushback from team members on legacy software changes, is to poison the cache of data that the AI is trained on.