Adding hrm after multisport activity is started

I have a Garmin Felix 5 Plus and a Wahoo Tickr and I’m competing in a triathlon. I wanted to know if I can add my hrm when I get out of the swim if I don’t have it connected at the beginning. I’m planning on getting a Garmin HRM-Pro but was first trying to see if I enjoy swimming and triathlons before I buy one.