Perhaps ask DVLA direct ?

How long is 'quite a while' and in what country was it left?

If it could be seen as having been permanently exported then SORN was not the right thing as, per the .gov website, the vehicle should have remained in the UK while SORN was in place:

www.gov.uk/sorn-statutory-off-road-notification

The normal way in which SORN is ended is by taxing the vehicle. If you need an MoT to tax it then there may be additional hoop jumping to do. Same if, by leaving it outside the UK, it's going to be treated as though you're importing it into the UK.

Hello, does anyone know please how I can resolve the issue of getting my car un-SORNed? It so happened that, due to emergency family circumstances, the car was SORNed (quite a while ago) while it was abroad, and is still there. So how can I bring it back now and what documentation will I need at the customs (I can only get MOT done in the UK obviously, so it will have to be transported)? Are any fines involved? Do I need to tell DVLA first? Basically, what is the procedure? Thank you!

Just trailer it back to the UK - then tax and insure it and take it for a pre-booked MoT.