You must register with a United States PRO to collect royalties in the United States on your behalf. In the United States, there are four different PROs: ASCAP, BMI, SESAC, and GMR.
Anyone can join ASCAP and BMI. SESAC and GMR are by invitation only.
Here are links to the PRO’s you can choose that do not require an invitation:
BMI - https://www.bmi.com/
ASCAP - https://www.ascap.com/