What should one do if they become in a state of major ritual impurity (junub) and the time for Fajr prayer has begun while they are in their university accommodation?

Purity is a condition for the validity of prayer. Whoever prays without purity, their prayer is invalid, based on the Almighty's saying: ﴿O you who have believed, do not approach prayer while you are intoxicated until you know what you are saying or in a state of major ritual impurity, except those passing through [a mosque], until you have washed [your whole body]. And if you are ill or on a journey or one of you comes from the place of relieving himself or you have contacted women and find no water, then seek clean earth and wipe over your faces and your hands [with it]. Indeed, Allah is ever Pardoning and Forgiving.﴾ And based on the Prophet's (PBUH) saying: "No prayer is accepted without purification." It is not permissible for a Muslim to pray while in a state of major ritual impurity as long as water is available to them and they do not fear harm from its use.