How can i set project completion dates manually?
Depends on where you are seeing these completion dates.
What are you looking at that shows them?
Most reporting on a completion date I know of is done in an app, and it is calculated from the data on the issues, it can not be entered because to do so would tell people that your estimates are wrong or your project is going to fail.
It looks like you're new here. Sign in or register to get started.