The procedure for what should happen if your child gets covid during exam season is here: www.tes.com/magazine/analysis/secondary/exams-2022-what-happens-if-pupils-miss-exams-covid-19
"Specifically, if a student is unwell with coronavirus and has to miss their exam, then a JCQ self-certification form 14 needs to be completed.
This form should be given to the student and parents or carers to be filled out by both the student and the parent or carer, and then returned so that it can be verified by the school or college (referred to as the "centre") before being submitted* *to the relevant exam board as part of the special consideration application.
The form can be filled out on a computer, however, the signature must be handwritten and electronic signatures will not be accepted.
Although there won't be an expectation for you to provide any proof that you have contracted Covid-19, the DfE does suggest taking a photograph of a positive test result if that is possible"
If a student misses exams, so long as they have completed 25% of the assessment they can still be awarded a grade based on the exams they have sat.
This is the same process as for other illnesses.
Re covid isolation, the DfE says
"I have taken a COVID-19 test under the direction of my GP and have a positive test result, what should I do?
The UKHSA guidance is that you stay at home and avoid contact with others for 3 days (if 18 and under) or 5 days (if 19 or older) after the day you took the test.
Your centre will ask you to self-certify the reason for absence using Form 14. You are not required to provide proof of a test but could keep a record of the test, such as a photograph, as evidence if it is available.
Your centre will then submit an online application for special consideration to the relevant awarding bodies using the category ‘absent candidate’"
educationhub.blog.gov.uk/2022/04/12/everything-you-need-to-know-about-covid-measures-during-exams-this-summer/