The lesson does cover this - have another look at the use of indirect object pronouns section.

It is only expressed as  ‘à qqn’, when ‘qqn’ is represented by a noun/name. Once you introduce a pronoun to be the ‘qqn’ as the indirect object, it takes its position before the verb as an indirect object pronoun, as in the standard usage and word order in French. 

Eg “ Tu rappelles Audrey Hepburn à Pierre. Oui, c’est absolument vrai. Tu lui rappelles Audrey Hepburn. “

The links below cover the use and position of indirect object pronouns :

https://progress.lawlessfrench.com/my-languages/french/glossary/3 

Using lui/leur = him or her/them (French Indirect Object Pronouns) 

Position of French Object Pronouns - with simple tenses