What you need is run a command on vSphere ESXi host to reclaim deleted blocks on thin provisioned LUNs, take a look: VMware KB: Using esxcli in vSphere 5.5 and 6.0 to reclaim VMFS deleted blocks on thin-provisioned LUNs
For better understand, take a look here: VAAI Thin Provisioning Block Reclaim/UNMAP In Action - VMware vSphere Blog - VMware Blogs