Yes, on the Settings page.
NOTE - this will restrict what data the user can see. So if you lock a user to a certain Purchase Flow, they will then only be able to see the Events and Channels connected to it, along with Orders that have only been made through the Channel(s) connected to that Purchase Flow.
Follow these steps:
1. Go to the Settings page and then the Team Settings tab
2. Click the pencil icon next to the user
3. On the pop-up, click the toggle next to Would you like to restrict their access to certain purchase flows?
4. Select the Purchase Flow from the dropdown and click Apply