I want to put an semicolon in his sentence, but I am not sure it is right.
Hi, SCM deployed this; it is ready for testing.
Also, could a colon be used in place of the semi-colon?
Yes, a semicolon is appropriate there. That sentence is joining two independent clauses without using a conjunction. It could be rewritten as two sentences:
SCM deployed this. It is ready for testing.
or as one sentence with a conjunction:
SCM deployed this, and it is ready for testing.
When both of those are true, a semi-colon may be used.
The semi-colon stresses the independence of the two parts more than the version with and, but stresses their connection more than the version with two separate sentences.
By contrast, a colon may be used for several things, but not in the example.
A colon can be used for several purposes:
Some people use colons to join independent clauses that are parallel in form. I do not favor this, but in any case it does not apply to the example.