To give learners the ability to retake a training you can use the Voluntary Retake option or the capabilities of the 'Certificate Expiry' settings in the Settings section while creating/editing the training. For example, you can set 365 days after the training completion in the corresponding field.
After 365 days the certificate status will be changed to 'Expired' and the user will be able to retake the training after the certificate expiry.
You can allow users to retake the training before the certificate expiry. Go to the LMS365 Admin Center > Catalog Settings > Notifications > Certificate Expiry Reminder template. Scroll a bit and in the 'Send Reminder Emails' field set the number of days when users will be able to see the 'Retake' button on the Dashboard - by default 60 days before the certificate expiry and the certificate status for the users will be 'Expiring'.
It is possible for users to have several certificates with the 'Expired' status (see the screenshot below).
To retake the training user should go to the training home page and press the 'Retake' button. The progress will be reset, the training status will be changed to 'Not Started'.