Im getting an error as my xConnect certificate appears to have expired today! Im a little suspicious by those dates as it would appear to be valid from Feb 2018 to today. Does this sound possible and would I use SIF to create a new one?
Assuming it's expired you can easily create a new certificate using Windows Powershell by running the following command(so no need of SIF just for that part):
New-SelfSignedCertificate –DnsName -CertStoreLocation “cert:\LocalMachine\My”
This is for self signed certificates. After you run that you will get the thumbprint of it, so just make sure you update the connection string and the AppSettings.config file, under the xconnect folder which is normally something like "myxconnectroot\App_Config\AppSettings.config"