Your members have the ability to reset their account passwords themselves but if they're having trouble doing it, don't panic, it's easy enough to do within the cms.
1. Login to the CMS.
2. Click on 'Members' down the left hand navigation.
3. Locate the member in question and click on their profile:
4. Click the three dots to the top right hand corner of the page:
5. Click 'send password reset' and it's done!