If you declined a lead for any reason, but then change your mind and decide the lead may be a suitable prospect, the only way to place them back into the leads dashboard is to re-enter their information and pre-qualify them using the Add Lead button. However, you will need to do so with a different email address for the tenant lead than the one used the first time around because the Tenant Turner software does not allow the same contact information to be entered multiple times (so you don't get duplicates). Once you have added the lead you will be able to schedule or confirm a viewing as normal.
As a best practice, don't decline a lead unless you really know you do not want to rent to him or her. If you want to just hide a lead from your Leads page, archive the lead and set your Leads page to hide archived leads.