How do you find contact info for collection agencies on credit report?

I have a couple of old (small) collections on my credit report that I’d like to clear up, but it just shows the name of the collection agency and a partial account number. How do I get contact and account information for these collection agencies so I can find out more information on these debts and pay them off or dispute them as needed? Would the credit reporting agencies have this information?
Thanks for any help!

I recently pulled my credit reports and it shows any accounts that went into collections/late payments within the first third of the report. It will list the OC or CA, the account number, and mailing address for each OC/CA.

The bureaus will have this information as well.