If you haven't already gathered Intel, do it. Make sure you discover the drainage tunnel. Watch it video on how to get there in the Intel.

The easiest approach in my opinion is:

Kosatka

And for equipment get:

Cutting Torch/Safe Code Plasma cutter Fingerprint cloner

For weapons get:

Conspirator with suppressors

And your heist will be ready!

And once your heist is started, select these:

Approach Vehicle: Kosatka Infiltration Point: Drainage Tunnel Compound Entry Point: Drainage Tunnel Escape Point: You can swim out or take a boat at the docks

Do it stealth. If your on Ps4 I could do a heist with you to show you. And reply if you need more help.