How are prayers "patched up"?

"Patching" the prayer means rectifying and addressing any deficiencies that occurred in it. If the increase in prayer was due to forgetfulness, or the omission of a confirmed Sunnah was due to forgetfulness, it is rectified by the prostration of forgetfulness (sujud al-sahw). However, the omission of a condition (shart) or a pillar (rukn) is not rectified by the prostration of forgetfulness; rather, it must be performed if it was omitted due to forgetfulness. If it was omitted intentionally, the prayer becomes invalid.