How to set consequences without being a landlord
Set consequences tied to the actual agreement: repay a shared cost, lose access to an optional shared purchase, take an extra chore, or begin a replacement and move-out process allowed by the lease. State them before the next violation when possible.
Do not change locks, remove belongings, shut off utilities, or threaten eviction. Co-tenants and roommates do not gain landlord powers through frustration.
For serious or repeating violations, involve the lease-holder, landlord, mediator, or legal resource as appropriate.