Comparing data in two columns and setting a value

Hello,

I'm comparing data in a very big database. and want to assign a value to matching data. For example

A B c
tenant code tenant name name
con1 john smith jane long
con2 terry mitch john smith
con3 jane long terry mitch

so john smith has the code of con1 and terry mitch is con2 in column c are numerous lease charges for them but they aren't in any order I would like to enter their code in column d that they have assigned to them from column a. how do I do this? so i'm looking for their name in column b and then assigning the value to them from column a.