Since the server pushes update notice to different serial numbers by batches, it may take some days for you to receive the FOTA notice. Thanks for your patience. You may tap “System updates” in [Settings] >[System] to check if there is new firmware available. Or, you can also try to manually update firmware by referring to the following link. How to update firmware on my phone?
【Release Note】 Update security patch to 2019-10 Update apn table to v258