To allow only one agent in the robots.txt file, you can use the "User-agent" directive followed by the name of the agent you want to allow. You can then use the "Disallow" directive to specify any directories or files that should be disallowed for that particular agent.
Here's an example of how the syntax would look like in the robots.txt file:
User-agent: AgentName Disallow: /path/to/disallowed-directory/ Disallow: /path/to/disallowed-file.html
Replace "AgentName" with the name of the agent you want to allow access to your website. You can specify multiple "Disallow" directives to block access to specific directories or files.
Remember to place the robots.txt file at the root of your website directory for it to be accessible to the web crawlers.