Overall time complexity of Heuristical Algorithm for travelling salesman problem [TSP]
Any algorithm that first does $A$ of work and then $B$ of work will have done a total of $A+B$ of work. It doesn't matter what the algorithm is, or what $A$ or $B$ are.

You might be getting confused by steps that look complicated and/or by the fact that $A$ and $B$ are expressed in terms of $\Theta$. For this reason and in general, it is a good idea to try to compute $A+B$ as well as possible, and then finally expressing the sum in terms of Big Oh. Otherwise, you run the risk of performing voodoo, and not really understanding what $\Theta$ means.