Any communal project is a marathon rather than a sprint: It’s important to be able to step back and trust your collaborators to follow the plans you’ve agreed upon, but when stuff falls through you need to be there to pick up the slack – and plans always shift, since life happens ...
If it’s too loose you’ll find adjusters at the end of the swing arm that will allow you to tighten up the slack. Your chain will go slack over time naturally.Check the chain and the sprocket for any obvious signs of wear, e.g. links look worn, sprocket teeth look worn, etc....