Avii,

you can use below formula to get the result you are looking for.
IFERROR(VLOOKUP(C3,A:B,2,FALSE),"")
Basically copy and paste the formula in column D. It will show blank if there is no value in but as soon as you enter the value, it will show you the agent name. Let me know if this help or if you need further help.

IFERROR(VLOOKUP(C3,A:B,2,FALSE),"")
A B C D
Dealer# Agent Dealer# Result
720486 AART
720491 BCCD 720491 BCCD
720496 SISI
720501 PRUF
720506 PARA
720511 PROF
720516 TOSS 720516 TOSS
720521 TFIT
720526 DOTD
720531 DHTD