Question

The new equipment just arrived this morning so the technician will come and set it
up tomorrow.
where should the comma​

Answer 1

morning, so the technician will come and

Answer 2

The new equipment just arrived this morning, so the technician will come and set it up tomorrow.

I have added the comma before so, as it is joining two independent clauses.

The  new equipment just arrived this morning - is one clause

The technician will come and set it up tomorrow - is a second clause

These two clauses are stand alone sentences.