With limited knowledge about the project and the team, here are my two cents: project management.
For example, ask your team to break down the tasks and provide a schedule for each task, and try to help them follow the schedule. If a task is taking way too long, ask them to break down it again. Remember to ask them to explain why they plan it like that.
Make sure you and your team have enough communication so you all know what need to do and what NOT to do. If your teammate is doing thing that is not in the scope, discuss with them and make the decision whether to support them or ask them to follow your request.
For example, ask your team to break down the tasks and provide a schedule for each task, and try to help them follow the schedule. If a task is taking way too long, ask them to break down it again. Remember to ask them to explain why they plan it like that.
Make sure you and your team have enough communication so you all know what need to do and what NOT to do. If your teammate is doing thing that is not in the scope, discuss with them and make the decision whether to support them or ask them to follow your request.
Rinse and repeat.