Anyone who has their hair coloured professionally will be unable to visit their salon for the foreseeable future. This means that people will have 2 choices: colour their hair at home using products purchased from a shop or let their hair grow out to its natural colour.
My advice is to avoid using permanent tint from a box as the results could mean a full-colour correction when things get back to some form of reality. Instead, use a temporary product that will cover your roots without doing any harm. The best one I’ve seen is called Magic Retouch Root Touch Up by L’Oreal. Here’s a link to their web page: https://www.loreal-paris.co.uk/products/hair-colour/root-touch-up
The product comes in several colours which will be suitable for most people. There are 2 types, a spray version and a concealer brush system. They’re easy and quick to apply and last until your hair is next washed.
If you have highlights, if possible, chose a tone that is a little closer to your highlights than to your natural hair colour, this will help to minimise a look of re-growth.
There probably are other similar products available but I’ve personally seen the results of this one, so am able to recommend it.
A word of warning, don’t have the product on your hair the day you come to the salon to have it done professionally. I’ve found that it blocks the professional tint and reduces coverage.
I hope this helps.