أحسن الله إليكم Sheikh, if a revert is praying alone but hasn't memorized what to say in the salah so they just say subhanAllah the whole time, how many times should they say subhanAllah in each part of the salah?

In place of al-Fatihah he says subhan Allah, wal hamdu lillah, wa la ilaha illa Allah, wallahu akbar, wa la hawla wa la quwwata illa billah, because the Prophet ﷺ taught exactly this to a man who could not recite (reported by Abu Dawud and al-Nasa'i; graded sahih by Ibn Hibban). In the rukuʿ he says subhana rabbiya al-ʿazim and in the sujud subhana rabbiya al-aʿla three times, and his prayer is valid while he learns, so do not overburden him.