Urgent help needed for my friend!!!!

Hello,
I am writing on behalf of someone who came to the UK for studies at age 17 in the year 2014- 2017and left after their degree four years later. The person returned to the UK again for masters in 2019 but due to unforeseen circumstances and financial restraint was not able to complete the masters. Got married to a British citizen and again was not able to legalise their status. The partner was away for years. The marriage was nullified after three years.
Now the person is with an Irish Citizen but the person has now overstayed in the UK. Is there any law that binds them to be married outside the UK that can be applied in the UK to help legalise their status or is there any advice on how to legalise in the Uk.
Thanks