The seller should have sent a letter naming you as the new owner and informing them of the pending transaction.
Here's the letter I use as the buyer, which should complement the seller's letter:
Dear (tenant):
We are excited to announce that our company is in the final stages of purchasing the building within which you reside, and I’ll begin managing the property on August 12, 2022. Being a local company, providing quality housing and great service is very important to us. I look forward to continuing to maintain your address with the same pride and quality that Ms. Peterson has taken in it over the past 19 years.
We are hereby cancelling your existing month-to-month tenancy effective September 31, 2022. Enclosed in this envelope is a new month-to-month lease agreement for you to sign, effective for October 1, 2022. In the meantime, please completely fill out both the Rental Application (included with this letter) and the Lease Agreement. I will make arrangements to come by and go over the lease with you sometime next week.
This new lease will provide you with important information regarding our company’s policies. This lease does not change the length of your lease term (month-to-month); it simply updates relevant matters now that I will be assisting you with your housing needs.
Beginning with rent for the month of September, please pay your rent by depositing the entire amount into the following bank account at (your) Bank: account # 123456; routing # 123456. We do not accept rent checks at our P.O. Box; rent can only be paid by bank deposit.
For your convenience, the nearest location to your home is 123 Main Street, (City), or you can execute a bank-to-bank transfer using the routing number provided.
If you have any questions, concerns or maintenance issues, you may call or text my cell phone at (your business number), or you may email me at the address listed at the top of this notice.
Please don’t hesitate to contact me with any questions about this transition or any other pertinent issue.
Sincerely,
(you)