The process of installing Wildcard SSL in IIS is start after creating CSR key. If you are not familiar on how to create CSR key for wildcard ssl then click here.
When you request your SSL from Certificate authority, you will get email of SSL Certificate.
• Copy SSL Certificate from email including the –BEGIN CERTIFICATE ---and ----END CERTIFICATE link
• Save this text as domain.crt (replace your domain with your domain name)
• Start IIS Manager
• Click on Server Name >> double click on Server Certificates
• Click on Complete Certificate Request from right your right side
• Browse the Certificate file (domain.crt) and fill friendly user name
• Click on Ok
Now you’re Wildcard SSL is installed properly on your server. After installing your Wildcard SSL in your server you need to build this SSL with your website
Please follow this link to set up your wildcard ssl in IIS: HERE