Is it permissible to make up the Asr prayer? And what should I do if I miss it?

It is not permissible to delay the prayer beyond its appointed time except for a legitimate excuse, such as sleep or forgetfulness. It must be made up immediately, along with repentance and seeking forgiveness, for Allah (the Exalted) says: (Indeed, prayer has been decreed upon the believers a book [to be observed at] fixed times) and the Prophet (peace and blessings be upon him) said: "Whoever forgets a prayer or sleeps through it, let him pray it when he remembers it. There is no expiation for it except that."