Change Cell Text Value based on another cells

Hi guys

Im having a really hard time on this, and i hope i can explain:
I need to control the installations on my company so on my file i have the status collumn where it either be: Assigned, Started or Completed.

On another collumn I have the TT Number, which means that for every Started task there is a TT Assigned to it.

So i need a formula that changes automatically the Status to Started everytime a TT is inserted on a cell. And if no TT is inserted it should maintain the Assigned Status.

I have tried with macros, Logical formulas, but no success.
Thnak you in advance.

Sorry for the late reply, timezone issues.
I have tested and it worked fine.
Many thanks!