XF 1.3 I need help with this error

i subbmitted my site for SEO and it give me a error telling me to make a robots.txt can anyone help me fix this error please

Error :
The following errors and warnings highlight issues that may cause search engines to misundertand or not index your website correctly.
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  • Empty or missing robots.txt. All search engines are looking for this file.
  • Found errors with this web page that can cause problems for search engines.
  • No major warnings to report.
Our free tools found at the bottom of this page will provide more details and help you correct many problems that keep you from ranking high in search results.