create a host wide redirect using IIS Manager. Select URL Rewrite, Add Rule(s)…, and Blank rule.
Name:
Redirect to HTTPS
Match URL
Requested URL: Matches the Pattern
Using: Wildcards
Pattern: *
Ignore case: Checked
Conditions
Logical grouping: Match Any
Condition input: {HTTPS}
Check if input string: Matches the Pattern
Pattern: OFF
Ignore case: Checked
Track capture groups across conditions: Not checked
Server Variables
Leave blank.
Action
Action type: Redirect
Redirect URL: https://{HTTP_HOST}{REQUEST_URI}
Append query string: Not checked
Redirect type: Permanent (301)
Apply the rule and run IISReset (or click Restart in the IIS Manager)
https://serverfault.com/questions/893315/best-way-to-redirect-all-http-to-https-in-iis