All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
Firstly, there is no harm in creating a Facebook page or a YouTube channel for this purpose (promoting health and fitness). It is better, though, that someone else, other than the caller to Allah creates it, or that he exercises general supervision over it if needed so that he would devote his time and effort to what is more important for a man of his position, namely Daʻwah (calling to Allah) activities and edifying people on Islam.
If the mentioned channel displays videos of people revealing their ʻAwrah, then this is impermissible in the Shariah. What should be done is to give him advice in this regard and remind him of Allah.
Allah knows best.