1. Copy the thumbprint from existing self-signed certificate:

Get-ExchangeCertificate -DomainName your.fucking.domain

2. Generate a new self-signed certificate:

Get-ExchangeCertificate -thumbprint “copy of your certificate number” | New-ExchangeCertificate

3. Enable the new certificate for IIS:

Enable-ExchangeCertificate -thumbprint “copy of your new certificate number” -services IIS