I'm assuming this is a shared hosting plan. In that case, this section of the FAQs applies:
It seems like GoDaddy does not allow you to upload a certificate and does not offer a one-click integration with Let's Encrypt, so your options are basically:
Switch to a hosting provider that supports Let's Encrypt natively (see list linked above)
Upgrade to a hosting plan that offers paid SSL (or one that supports uploading third-party certificates, if available, and then use the manual plugin as described above)