How to validate workitems in saleforce devops center beta. Iam unable to see the validation option

Hi team,

1) So I was trying to validate the work item to the higher environment, but I can't see any option for that. If I click "promote change in the pipeline," it is automatically deploying changes to the next environment. Please help me to validate the changes.
2) Back sync
When I want to back-promote the changes, it is simply saying "sync the changes." If we sync the changes, how can we know which work items are back-syncing? If we sync like that, there is a chance of overwriting other developers' changes, right? So please guide me how we can see in a proper way to sync the changes

These questions refers to Salesforce devops center (Beta version)