Good day Olivier22

Yes, it is possible to add a favcon on your K2 forms, please follow this link: https://community.k2.com/t5/K2-Blackpearl-Forum-Posts/Favicon-in-K2-SmartForms/td-p/82902 for a detailed process on adding it. On the "href" please enter the exact location(URL) of your icon

I hope this is useful towards your solution, please provide kudo or solution should it work.

Thank you

Kind regards

Thabang