You could try using the Function PU_MAX. Just plug in the name of your vendor master table and the name of the column that contains the PO Entry dates.
Then Celonis would return the largest value of PO Entry Date corresponding to every row the Vendor master table.
Depending on how your data model is set up you might get the error “TABLE X is not a parent of Table Y”. In that case either try using a second PU_MAX function inside the other one or write back with more details about your process model and we’ll try to help you further.