How does a COVID-19 patient, in quarantine, pray if he had a wet dream and ejaculated with very cold water, and there is nothing available but a tap and a Western-style toilet?

If the use of water is harmful due to its coldness, based on previous experience or the advice of a trustworthy doctor, then it is permissible to perform tayammum for prayer and other acts requiring ritual purity, until one is able to use water. This is supported by the action of Amr ibn al-Aas (may Allah be pleased with him) when he performed tayammum and led the people in prayer on an extremely cold night after he became ritually impure (junub). If a person fears intense cold and is unable to heat the water or use it safely, then it is permissible for him to perform tayammum. It is not permissible to abandon prayer as long as one is of sound mind, and one must make up the prayers that were missed.