How to contact firms to look for an off-cycle internship or network for FT?

I'm currently a senior in college, interned this summer in a real estate-adjacent field, looking to find a full time position on the buy-side for after I graduate in May. How should I go about contacting firms to try and network with them, do I focus on alumni from my school? How high up should the employees I reach out to be? Should I go through Linkedin or Email? As you can see, I'm new to cold-emailing and could use any advice you guys have.

Thanks in advance.