Adding VAT to my invoicing & Statements etc

Working on Access 365 database. I have a bespoke programme that generates bills and statements for my ironing service. We were VAT registered pre Covid. Post Covid we dropped below the threshold and had the VAT element removed . 5 years later we are back at the threshold so need to include VAT again. It was described as a simple job last time, not taking many hours - but its outside my capability.
I cannot attach the file as its not supported, sorry