If you have a standard policy in place you need to follow the proper notification process outlined in the flood regulations. That is send the 45 day notice and allow the borrower time to obtain a policy. You may not force place or charge them for insurance during that time. On day 46 you should force place if they haven’t obtained insurance. Here’s a link to the regulation: https://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&SID=3d5de1e4a10cfcd995b50851357bba4d&rgn=div8&view=text&node=12:1.0.1.1.20.0.8.7&idno=12
If you have an MPPP policy in place you may renew this policy on it’s renewal date rather than waiting until 45 days after it expires. But you need to follow the MPPP notification process which includes letters that go out 45 days before the policy is set to expire, 15 days before it is set to expire, and a final letter when the policy is renewed (the latter two are only required in the event the borrower doesn’t purchase the required insurance.) You can find the MPPP notification process here in Addendum 2: https://www.fema.gov/library/viewRecord.do?id=3820