If you have lost a device with client certificate installed, ask your administrator to change the password, to revoke the client certificate, and then to reissue a new one.
The administrator who received the request should refer to the following page to perform the actions:
When Users Have Lost Their Devices with Client Certificates Installed

The Client Certificate Authentication will become unavailable on all the devices on which the same certificate is installed.
In addition, the notifications from mobile apps, such as kintone Mobile or KUNAI, using the Client Certificate Authentication will not be displayed on the devices.
Reissue a client certificate and install it on the devices again.