Any advice on how to walk on at a d3 swim school?

Hi, I’m currently a senior male with a 1510 sat and 3.59 unweighted 4.29 weighted gpa. My best events are the 100 back (53.39), 200 free (1:46.63) and 50 free (22.48). Also, if anybody could drop some suggestions that would be great as well! Thanks in advance!

Email coaches at the schools of interest and ask about the process to walk on.

Agree with the above. But first I would also compare your times to the times of people already on the team or D3 standards (should be able to find some guidance online) to determine if you would be competitive.