A Muslim is to pray to the best of his ability, the best he can, due to the statement of the Prophet, may Allaah raise his rank and grant him peace, “A sick person prays standing. If he is unable, then he may pray sitting. If he is unable, then he may pray [laying] on his side.”
Text taken from brother Moosaa Richardson’s website.

How to Pray in a Chair When Needed (Shaykh Saalih Al-Fowzaan)
Moosaa Richardson

Praying in Congregation on a Chair for One Who is Unable to Stand or Finds it Difficult ― How does he Line up the Chair with the Row?
Abu Khadeejah

Observing prayer (salat) in a sitting position – The permanent committee for Fatawa
Salafi Nigeria

With a Video
How To Pray Salat In A Chair | Shamsi
DUS Dawah