1. To change the access, remove the form from Microsoft Teams. Then click the plus to add a new TAB.
2. Choose the Forms Application.
3. Add an existing form, choose your form and make sure the drop down is Collect responses. Press the save button to add the form to the team.
4. Now your form will only accept responses and users cannot modify or share the form.
5. You can also rename and move your tab if required.