I have a form to add the data to the database. I have to create an update feature now, so I need to know if I can use the same form that I have created to add data to database or make another form for the update feature. What is the best practice? Should I have to implement update feature as a separate component or that's not necessary?
As long as they are really similar (e.g. they won't have some extra validation rules which will enforce you to write many if inside the component) it is good practice to reuse components wherever it is possible.
If you have different endpoints for creating/updating resource you can easily pass custom onSubmit function to your form component which will call proper service method.
<your-form (onSubmit)="add(...)">
</your-form>
<your-form (onSubmit)="update(...)">
</your-form>