I've just home dyed my hair from dark blonde to a supposed light ash blonde its gone light ginger is it safe to re do it a different colour?

The same thing happened to me a few years ago.
Are the ends darker and more ginger/brassy than the roots?
I'd recommend giving it a good conditioning or leave in hair mask, then bleach using a self-mix variety which can be bought in pharmacies.
then, the best thing to do would be apply to the ends first, and then the roots and leave as long as it takes to see the desired results. usually no less than 90 minutes for dark hair, but probably won't take too long because it's been previously lightened.
If it's still a bit ginger you could try using some toner which balances out the ginger because it's a purple sort of tone, then you could either leave it as it is, or use another packet dye of an ash blonde or whatever over the top a few days later and it should be fine.