HELLO
Enfaite c'est simple il faut juste utiliser "could" qui est can au passé (=prétérit)
1) When he was younger he was clever , he could stand on his head
2) At six years old he could sing quite well
3) He told me that he could speak four different languages
4) He couldn't come yesterday , he was ill
5) When you were in London could you call her ?
Bonne journée