If your Nokia 97 mini flashes with a message with description as SIM memory is full, then you can try to clearing the SIM messages. This can be accessed by navigating to Menu –> Messages –> Options and selecting SIM messages. If you need the SIM messages, then make sure to take a backup by copying the messages to the Inbox folder. And then select all your SIM messages by using Mark All option and click on Delete to clear all the messages.
This should clear the flash message at the top of your Nokia 97 mini.