An entire Membership type can be marked as a trial, so you can have multiple different trial plans within the Membership type.
1. Go to Manage > Memberships
2. Open the Membership that you want to tag as a Trial
3. Click the 'Advanced' button
4. Turn on the toggle for 'Trial'
5. Click Save
A client's status will only be updated to Trial if
1. They had a status of Lead when they purchased/received the membership
2. The Membership was marked as a trial when they purchased/received it. If the membership type is updated after they get it, their status will not be updated.