Login to the Certificate provider and renew the existing certificates. Download the PFX version of the new certificate.
Follow these instructions to encode the certificate into Base 64 text.
Open Terraform and navigate to the Workspace -> Variables for whichever workspace/environment you are renewing the certificate for.
Edit the "Cert" variable and paste in the base 64 encoded text from the certificate.
Edit the "certPassword" variable if there is one and paste the password for the certificate. Not every certificate requires a cert password. If that is the case, skip this step.