New landlord(payment, contact info etc.)

[Christopher Krueger]

I recently bought a duplex and went in yesterday to meet the tenants to inform them that the property was under new management. Safe to say it didn’t go very well as the previous property management company didn’t inform them that the property was being sold. Other then contacting that company and asking them to inform the tenants that the property has changed ownership. What is the best way to go about getting all of their contact information and start collecting rent. Is there a good app to use or just mail as this is my first property and am still trying to figure things out?