If you don't remember your last period, please read the following article: What can I do when I do not remember when my last period was?
If you need further assistance, please contact our technical support. The easiest way to do this is to use the CONTACT SUPPORT function in the femSense app MENU.
If you have any error messages from the app, please attach a screenshot of the error message to your mail to support. This will make finding a solution to your problem easier.